aaron- I looked into the same thing- building these out for people- and the biggest hurdle is LIABILITY. You are basiaclly putting together a vehicle from scratch, and unless you are a certified bike mechanic as well as a small engine tech, you are taking other people's lives in your hands. People in this country like to sue people. So if you were to start an actual legit business doing the build outs, you would need an ironclad waiver of liability if anything mechanically should go wrong or if the person injures themselves..
Also, I posted mine up on Craigslist here locally trying to do the same thing (indie biz) and all I got were other people asking where I got the kit from, if I had this or that spare part, or they would mysteriously disappear and not reply back once I told them there was a waiver of liability that needed to be signed in order to purchase..
I was building mine out with lights and blinkers to appease local laws too, so after parts were all factored in, it was $580-$620 MY cost on the new bike/new engine/lights, and people didn't bite at a MB that ran $800, which really for the amount of labor involved wasn't a lot for labor.
If you can figure out a way, let me know. Chances are you might have some competition though as I'm moving back to Chicago in the not to distant future! haha...