The Norvel Big Mig is a good choice ( alot will argue with me though) if you want inexpensive. Don't put a pipe on it or try to get the last few RPM's out of it and it will run fine, start easy, and last for quite a while. Run 3 or 4 tanks thru it before you toss it into the air and it should be fine. I've got 4 of them and have not had the problems that have been reported because, I think, I use the stock muffler and tune it slightly conservatively. Yes, the FX for $30 more is a better engine but the Norvel is close.

Just my opinion,

JESTER