I doubt that $300 is going take you very far toward getting tooled up for frame building and painting. Even after you get tooled up, what are you going to do with it? How many bike frames do you envision yourself making?
The wheelbuilding route makes a lot more sense to me. Frankly, I have no trouble with using pre-ridden hubs but I'd advise buying brand new rims and I wouldn't mess with the cheapo's either. If you want to build a good wheel you have to start with a good rim.