OK its going to be a “small” 3D printer and not the most accurate. But its cheap, and I am pretty sure you can get it cheaper too (author is down to $55, I think I could get it down to $45). Reason I say that is the motor controllers can be home built. And I have seen the pen go for $35. Still nice build for kids.
http://www.instructables.com/id/Super-Cheap-3D-Printer-From-CD-Rom-Drives/