Balsa is so soft a good hobby knife and a metal straight edge is all that's required for cutting out fins.
I'm very pleased wiht my Dremel saw blades for plywood, hardwoods even brass and copper, but they are a bear to control. I'd suggest one of the small table saws if your not comfortable cutting balsa fins with a knife. they get a much better finished cut and WAY better control. also much more expensive
I would be careful cutting balsa with any type of power tool, it is extremely soft and it is very easy to cut more than you mean to or to stray fromm a line you are trying to follow. I always use a knife for balsa, but if you made a jig to keep from straying you might be able to do it.
This is my gigantic table saw. The Elmer's is for scale. Huge isn't it? I cut everything on it from balsa to plywood as well as G10 with the included diamond edge blade. The G10 cuts like butter. All edges come out smooth if I take my time. If I were to buy one again I would probably go one size up but this one has done great for the about $35 I paid at Harbor Frieght.
I got it at http://www.harborfreight.com/ . The $75 one is the one I really wish I had bought instead but this one has done pretty much everything I've asked so far. One day I'll have to build an adjustable rip fence for it as thats what it really needs, the little widget it has with it is virtually useless.