Gampi, several people at my club fly the mini with the .25la.
The thunder tiger gp25 will also work.
Both are within your price range. If you go to extremeflight.com and see what the engine recommendations are, you will hopefully be able to discern good advise from the worthless babble above. The mini is as good as it gets at harrering. That and harrier rolls can be done under half throttle with either of these engines.