You can already buy ~90% of what you need to build a 3D printer from the Inventable’s store…
Extrusions for the frame
NEMA Motors (2 for Y, 1 for X, 1 for Z)
GT2 belts
Motor Brackets
Bearings, couplers, pulleys.
Arduino
Power Supply
Nuts, bolts… etc
All that’s missing is some smooth rods, heat bead, ramps 1.4 board and some type of hot-end.
The trick would be to build something BETTER then your standard i3 Prusa (google ‘Folger Tech 2020 i3’ to see an i3 built using Aluminum Extrusion as the frame).
IMHO… It would be a very hard market to enter. Printrbot, Ultimaker & Lulzbot (Aleph Objects) already create award winning open hardware printers with amazing support ($1k - $3k). You’d also have to compete with the do-it-yourself-for-cheap companies like Folger Tech (under $300), or the never ending i3 clones coming out of China (Geeetech, Monoprice… etc @ $350).