This is the second version of a small quad copter that I designed and built. It is designed so that the only power tool required to build it is a laser cutter.
You can get multicopter frames for cheap from a number of sources, but I wanted something that was more customizable and hackable. The cost to build the actual frame by itself for this quad (including glue, etc) is only about $50. The rest of the costs are probably similar to what it would cost to build a quadcopter using a commercially available frame kit. I also believe it to be more sturdy and easier/cheaper to repair than a lot of quad frames on the market. While learning to fly with version 1 of this quad, I crashed it repeatedly, several times into a tree. After several hard crashes I did break one of the motor mounts, but a little bit of wood glue and some clamps and it worked as good as new.
While I think this makes a fine first quadcopter for people (it was essentially my first), having some knowledge of building and flying RC vehicles will help. I've tried to be thorough in both documenting the build as well as providing sources for the materials and parts.
Let me know if you have any questions, problems or suggestions.