There are several models of DIY 3d printers around. The grandaddy is the reprap; CupCake and several others build and specialize the original design. The expensive parts cost around $350-400; the rest is printable on the machine itself for dirt cheap, if you can find someone to do it for you or you already own your first. Typically you can, for a price, and that's where the other $300 or so comes from.