The altitude record is held by a team called Go Fast, who passed the Kármán line, the internationally recognized "edge of space" at 100 km*. While that's only been done once, 30 km is not terribly uncommon among the really big flyers (which does not include me). The lower (and more reasonably priced) end of the high power hobby often sees one to two km flights and four or five now and then. Low or mid power tends to reach anywhere from 100 to 1000 meters.
There is an altitude limit for casual launches and waivers from the Federal Aviation Administration are required beyond that, each waiver having a specified altitude limit. The waivers are usually obtained by leaders of clubs that organize the high power launches, who deserve more credit for their effort than they frequently get. (Thank you, waiver holders!) Others can tell you far more about that process than I can, but I know it's not as hard as is might be.
* This is where you say "Holy crap!"