I guess I'll just go ahead and point out the work that SpaceX is doing as far as reusability and Dragon v2 go. If I had to guess, they probably wouldn't hit a billion on a human trip to Mars.
SpaceX and NASA are two TOTALLY different animals...
NASA is basically threatened by SpaceX but dependent upon it, thanks to COTS and, perhaps, (but nothing is written in stone yet!) CCICap (Commercial crew, basically-- the new acronym is about as clumsy as they come... don't see why they couldn't have kept calling it CCDev...)
SpaceX offered to develop a human rated all-liquid (effectively a modern-day do-over of Saturn V) for $3.5 billion dollars total development cost-- that's a GUARANTEED PRICE, not some typical big old-school NASA contractor "price plus" contract that basically pays them extra for going over budget and over schedule on the development, which is why NASA development programs are pretty much neverending budget sinks taking decades and costing billions with little/nothing to show for it. SpaceX effectively said, "Give us $3.5 billion and we'll deliver you a man-rated modern Saturn V in five years (IIRC on the schedule). If it costs more, we'll eat the difference."
NASA said, "Thanks, but no thanks." The basic reasoning is that SpaceX is the "new kid on the block" and they "don't really know or understand what it takes to do these really big projects. They don't have a proven track record like Boeing, Grumman, Lockheed/North American, Pratt & Whitney/Rocketdyne, ULA, ATK, etc. etc. etc..." (all the usual suspects BTW that normally get those fat billion dollar development contracts that run years over schedule and billions over budget and usually get canceled before anything flies). Plus, NASA doesn't want to "farm out" its rocket development-- nevermind that they haven't developed a successful flying vehicle since the shuttle in the early 1970's-- 40 years ago basically. Nevermind that the successful design and development and state of the art know-how now resides in industry, mainly among the aforementioned "favorite contractors" of NASA, especially in ULA which designed, developed, tested, and now flies the EELV's, Delta IV and Atlas V, for DOD and NASA.... (among others). No, former NASA Administrator Mike Griffin demanded (or at least readily endorsed the idea, same difference) that "only NASA could develop the next generation manned exploration space vehicle and booster" even though it required basically the complete reconstitution from scratch of the design and engineering organization and capabilities within NASA to do it "in-house", because MOST of the experienced engineering base is OUTSIDE NASA, NOT within it... (at least not in terms of booster design and development-- manned spacecraft, which basically is a PAYLOAD, YES... booster development, no...) Is it therefore any wonder that Ares I/V development was a basket case and SLS, although better (less ambitious) is going to take over a decade to get flying and will cost the better part of $40 BILLION dollars to develop??
Of course, the politicians like it that way. Had Columbia not disintegrated during reentry over Texas, they were QUITE content to fly shuttles until they literally fell apart... that was the plans NASA and Congress had before Columbia-- fly shuttles until AT LEAST 2020, recertify them to fly to 2030. NASA basically knew that it'd be a stretch to keep shuttles going to 2020 or much past that, and sooner or later they'd need a shuttle replacement, and a cheaper one at that, which is why they were developing the "Orbital Space Plane" (OSP) when Columbia disintegrated... it was a slow-roll shuttle successor program, since NASA couldn't get funding for a full-fledged development program for a shuttle replacement. Shuttle served Congressional interests perfectly-- to distribute pork to the "right contractors" in the "right Congressional districts" in the so-called "space states" (primarily Utah, Texas, Florida, and Alabama). So long as it was working correctly for that, operations and safety were no great concern of Congress, no matter how much rhetoric to the contrary.
Thankfully, NASA decided to let "commercial space" (ie, anything NOT directly under NASA control and budgeting) get a piece of the pie to resupply ISS, once it became clear that 1) it wasn't cost effective to spend $450 million to launch a shuttle hauling a few tons of supplies up to ISS all the time, 2) the Russian Progress couldn't resupply ISS alone, 2) the combination of the Progress, ESA's ATV, and Japan's HTV wouldn't be capable of keeping ISS supplied with the shuttle retired, 3) this meant that there would have to be SOME way of taking up the slack... thus basically COTS commercial resupply was a decision "forced on NASA by reality" more than a conscious choice over other possibilities. COTS provided the funds to bootstrap commercial space operations like SpaceX, and to an extent, Orbital Sciences Corporation (OSC) (which of course already had it's own small satellite launchers, primarily in Pegasus and repurposed ICBM's modified into launch vehicles (like Minotaur).
For now, NASA and its contractors are resting on the laurels and proclaiming from the rooftops, "rockets and space is HARD-- ONLY *we* (NASA and big time "old-space" companies that have been NASA/gov't "cost-plus" contractors for decades) can do it! These "kids" at SpaceX and commercial nu-space are a bunch of inexperienced, overeager, naive, and overambitious space cadets that don't understand just how hard it is! Only *we* can be trusted with the lives of astronauts and deep space missions and heavy lift and things like that..." Of course, truth is, SpaceX is learning fast... it's not an ancient bloated bureaucracy like NASA or top-heavy "military-industrial complex" old-space cost-plus contractor like most of the existing NASA contractor base that gets such programs like SLS development, etc... but instead they are a lean, mean, modernly organized and operating space company pioneering a "new way of doing business" and getting things done...
Now, let's play a little thought game... what's going to happen in a few years if SLS is still in development and testing and SpaceX is flying Falcon Heavies regularly and reliably to orbit hauling 70 tonne payloads, launching and landing reusable Falcon 9 stages, launching and returning astronauts from ISS under CCICap (commercial crew) (as well as any other "commercial users" that might pop up-- space tourists, Bigelow hotel flights, man-tended space industry, whatever), and flying payloads with Dragon, and tinkering with developing Red Dragon and working on how to land a Dragon on the Moon (manned or unmanned)... Let's say that SLS development is going swimmingly and a few test flights have been made, but it's still a couple years away from the first manned missions to *anywhere* other than test flights, and it becomes obvious that SLS has no payloads except Orion, and that without payloads it won't be doing ANYTHING. Furthermore, when it dawns on everyone that, since SLS is based on the same old super-expensive shuttle hardware (SSME's and SRB's, among others) and that now that SLS will REUSE NOTHING, but instead dump all those parts on the ocean floor offshore of Florida or in the South Pacific or Indian Ocean after burning most of those expensive parts into burnt cinders... that SLS WILL be THE most expensive launch system ever devised by man (shuttle notwithstanding-- the present record holder but which will be eclipsed by SLS costs due to the low flight rates and getting NOTHING back after each flight). Don't you think there are gonna be some hard questions asked??
There's gonna be a forehead slapping moment when public outrage at the expense of SLS/Orion becomes generally known and understood among the sleeping "public" (who only cares when their tax dollars are going to something they don't want instead of something they DO want) and Congress FINALLY has to face facts that are now the 800 pound gorilla in the room... When it's TOTALLY apparent to even the most slack-jawed politician that SLS/Orion is going to cost well in excess of a billion per launch, before mission costs, and that SpaceX can basically do ALMOST the same thing NASA is doing, just in a different way, for a small fraction of that.
After all, in the 6 years after the loss of Columbia, NASA spent over $9 billion bucks to develop a crew rocket that basically didn't work (Ares I), a super-mammoth HLV that was STILL not capable of launching everything needed (Ares V), and a new human deep space exploration spacecraft that had been stripped down to the bare bones of what was proposed (Orion). When the Constellation debacle was cancelled, NASA had Orion at CDR (ready to start bending metal, basically), Ares I was a basket case (although they "fudged" things to make it look like it was past PDR and they were making progress-- it was facing a number of huge issues and potential show-stoppers and was already YEARS behind schedule and billions over budget). Ares V was basically just a paper rocket, still unable to close the design due to additional requirements being shoved onto it due the anemic performance of Ares I. In the same time NASA spent $9 billion dollars and six years of largely WASTED effort, SpaceX developed a new human-capable (yet operated unmanned for COTS resupply) all-new spacecraft (Dragon), TWO new boosters (Falcon 1 and Falcon 9), and an all-new engine (Merlin) and took it through several different iterations and modifications to uprate its performance (from the original ablatively cooled Merlin design through the modern uprated Merlin "C" used on Falcon 9, with more upgrades in the offing). They did all that in about the same time period, and using only about a billion bucks or so... a pittance in terms of space development costs... (heck program OVERRUNS in most projects are more than that!)
I've had old-space pud-knockers whine, "you REALLY believe that SpaceX did ALL that for ONLY $1 Billion bucks??"... My reply is, "okay, let's play devils advocate-- lets say they WERE underestimating their actual expenses by a factor of three... Let's say they spent $3 Billion developing Dragon, Falcon 1, Falcon 9, and Merlin... that's STILL only ONE-THIRD what NASA *WASTED* on Ares I/V and Orion development, in the SAME TIME FRAME... It's STILL the biggest bargain around!"
Of course, time will tell... there's a lot still up in the air... NASA has, so far, its fat development contracts for SLS and Orion... that could change with a new Administration or major shakeup in Congress, or if something major happened... SpaceX is working hard to perfect vertical launch and landing via boostback or vertical powered landing downrange... they've been making remarkable progress, but they HAVE suffered setbacks recently, as most complex projects do. Time will tell if they succeed in making their idea of reusability work reliably, and if it's actually a money-making proposition that can cut launch costs as much as they say. They're making good progress on their 53 tonne-to-orbit launch vehicle, Falcon Heavy, but IT HASN'T FLOWN YET! Impossible to say how well it will work until it has a flight history. Falcon 9 operations seem to be going well, though there's the usual difficulties and setbacks that cause delays. Dragon is working well, and its modification into a crew ferry vehicle seems to be progressing well, but it hasn't flown in that configuration yet, so problems may still show up. On the NASA side, SLS is progressing well by most information we get, but again, it hasn't flown yet, and time will tell if there are more "teething problems" down the road to come that will delay the development. Costs are pretty easy to figure out will be substantially more than shuttle, due to a combination of lower flight rates and no reuse of anything. SLS also STILL has NO missions approved and budgeted other than some test and demonstration flights, and NO hardware approved or funded for development to do any missions.
So, things are in flux... but if I were a betting man, I'd put my money on SpaceX for sure, based on their past performance and NASA's past, current, and ongoing debacles...
Later! OL JR