ORIGINAL: MinnFlyer
Look at it this way:
You buy the weed wacker for $200. Then you need to take it apart. Then you throw away all of the non-engine parts. Now you need to make a prop adapter.
Unless you are a machinist with access to a lathe and milling machine, you'll have to have one made for you. I used to be a machinist and I can tell you that it won't come cheap.
Finally, you'll need to adapt the mounts to fit a firewall (Back to the machine shop).
Or... you can spend another $100 and get one of these, bolt it in and you're ready to go.
http://www3.towerhobbies.com/cgi-bin...&I=LXNRH4&P=SM
You can also spend 3 months building up a plane from a kit that you could buy as an ARF and have flying in one weekend. By the time you buy the covering and all the other goodies, the ARF is no more expensive than the kit. Yet I still buy the kit because I still like to dink with it, do it my own way, etc. Sometimes you gotta do it for the sake of having fun. And don't forget the marshmellows and a stick.