ORIGINAL: Ralphbf
The thing about conversions is that the cost to convert is about the same no matter what engine you choose.
Find a plane, then pick an engine to power it with would be a logical thing to do.
There are a lot of free engines out there.
And a lot of inexpensive air frames at swap meets.
I always end up doing that backwards. I will get a freebie or really cheap engine, get it running, then look for a plane to put it in.