Dotleon aka PM_ME_YOUR_MAINFRAME came up with a really cheap Ferris/Sweep alternative to test a 34-key setup:
Cheapis! A very cheap alternative to ferris and sweep. Good for experimenting with a 34 key layout. The PCB is under 100x100mm, so it can be ordered for $2 + shipping. I made this because I wanted to try 34 keys on a low budget – dotleon.
Specs
Unibody angled split (sides angled by 20 degrees)
34 keys
Compatible with MX, Kailh Choc v1 and Gateron low profile switches (soldered)
1n4148 SOD-323 diodes
19mm standard spacing
Pros: less than 100x100mm, reversible, so you can order less, needs only one Pro Micro (or alternative) – very cheap.
Cons: it has to be unibody, tenting is not possible, fragile without a plate as the Pro Micro keeps the two sides together.