I've followed the Keyboard.io Model 01 crowdfunding campaign (they have the best writeups!) with a lot of interest. I'd probably buy two of their keyboards if they'd offer a German keyboard layout. They are $329 each. For that price, I expect a perfect product. A keyboard that looks equally tempting (but involves a lot of soldering and other work) is the Dactyl keyboard ( https://github.com/adereth/dactyl-keyboard ).
You can fully customize the layout of the Keyboard.io and get blank keycaps https://community.keyboard.io/t/whats-the-latest-info-on-key...
You can get a barely used one for ~250 just watch their forums.
I've got one 1-2 months ago after playing with a Kinesis. The keyboard is really nice. The firmware and software ecosystem around it is powerful but still lacks usability (you write plugins in C although they have a really nice graphical interface to configure it). https://github.com/keyboardio/Kaleidoscope