Fully programmable, and just the PCB? GH60. Switch coverage for decent MX will run another $25 or so (Gateron) and keycap is varied, but iKBC / Vortex offers solid PBT options for $30. In total you should inch towards the $100 range with plate and stabilizers.
Anything prebuilt on the market will likely disappoint if you're looking for full programability. Of course, there are Tada68 kits too that are excellent value.