I bought a Funstar off a fellow club member for $10. Keeping in the spirit of that price, I put an old OS 46 LA engine on it. The plane will hover (at least for a while) on it!

You definately don't need to go overboard in sizing the engine for this plane. I would save the 50 SX for another project. A Thunder Tiger 46 Pro would be a good choice, and at an under $80 street price is quite a bargain.