So, I did ask this same question earlier in the "How To Become A Developer" -thread, but thought its worth of own thread. Im trying to find guides to make Teensy like board myself, as low cost possible.
Then I came across this site, and was amazed!
Stealth USB CapsLocker
And whats best of it, its programmable! He also provides PDF that has tiles set of PCB schematics ready.
Because Im not expert on this subject, Im trying to figure out the programmer adapter he used. If any of you have any info on that, please reply. Im still interested if any of you find other guides to produce such a device.