Perhaps the most interesting thread on Head-Fi.org is the DIY Electrostatic headphone thread. With cheap DIY CNC equipment now available, a whole world has been opened up. Orthodynamics or electrets could be done DIY’ed as well.
The thread creator, Chinsettawong, is very receptive to helping others and sharing his knowledge.
DIY CNC machining is an exploding area that has only become accessable to an amatuer in the last few years. With a little work, one can set up their tools for under $2k. Google searches can help too.
Head-fi.org: My DIY Electrostatic Headphones
Furthermore, here, some measurements are provided for Chinsettawong’s creations