Sorry if you don't find my site useful cipher, it's only getting better. However I didn't put my site on here to advertise, sure I'm promoting it, but I'm promoting it to show people what they can do to start making an income with 3D printers. Like this topic asks. And that's only 1 of infinite ways to do it. There's one thing for sure if you plan on making an extra income with 3D printers, and that's that you have to be creative.
I think it would be fun to design a simplistic 3D printer, print it, purchase the reprap kit or something similar, combine the two and put it online somewhere to see if it gets any hits. The only way you'll know if your idea is worth expanding is to start expanding. Just jump in. The only time better than today to start a 3D printer company was yesterday.