Getting back on Topic;

Yes commercial engines do cost more. In my case, much, much more. I have a 34cc Briggs and Stratton Four stroke Gas engine. I converted it from a Sears weedeater. The wacker (used from Ebay) was 100.00 with shipping. I paid Wackerenngines 18.00 with shipping for a hub. A buddy of mine made the 1/4 inch back plate and my band saw took care of the rest. I have a great running, dependable, (and oh boy does it sound good) engine for 118.00. Fuji, the only commercially availible four stroke engine that I know of for RC, has a wopping 799.00 on thiers. This engine does include an Electronic Ignition, but for 189.00 I could have that to. Even with the extra cost of EI, I would still only have 307.00 into the motor. Now,a savings of 490.00 is somewhat profound.
I do however agree with a comment that was posted way up there someplace, the real difference is how you feel about doing the conversion yourself. Its a great fun to play with these suckers and end up with something "I" built. And of course you can brag to friends how cheap it was. I have a feeling it really isnt about saving money to most of those that look down on conversions, I have a feeling it is all about bragging about how much they paid. To each thier own. Just go out and have fun.