Heh - I think you're describing the dream of almost every member on here, I see a few that have managed to pull it off too
They all have secrets
One of the charms about these bikes is that everyone builds different, other than the "complete with bike" kits some of the dealers provide it's a matter of diggin up good yet low cost bikes that take the conversion well and adding that "personal" touch. The basic builds are so easy my boss's eleven year old son built one himself in just three days, only using my bike as an example. Yet I'm shamed to say it took me almost three weeks to build mine and I've built powered bikes before lol
I'd recommend building just one or two to get the feel for it and selling them when they're done. That way you can learn the quirks, play with the bikes, and even test the local market. Having done that, you can buy engines in bulk lots (starting at ten) and build to suit.
I thought about it myself as they're none too common around here, mines been quite popular and I don't think I'd have any problem selling it. Yet I find I'd rather do that than be a dealer - build a bike, play with it for awhile and then sell it for my next. To build them in any quantity would take away from my playtime lol
More power to you though should you want to! Tooling is pretty basic to start with, of course the more you have the more you can do, welding is a damn handy skill. Defo give the dealer links around here a lookin' at