Interesting build. The author did the standard convert CDROMs into a mini CNC. Thenk put a 3D printing pen (looks like a generic 3Ddoodler) on it. I guess you can get generics for $50. toss in the arduino and controllers and you have under $100 in materials to build.
http://hackaday.com/2015/11/11/3d-printing-pen-and-cnc-machine-yields-cheap-3d-printer/