The Vortex aluminum Filco
case costs $150, and that is seen as inexpensive. The MKC case was $350, and while the build quality was better, it was still too expensive for most.
I would estimate $60-80 plus shipping for your switches. You want to buy around 100 switches, so you have a few extra "just in case."
If you just get the PCB, Teensy, diodes, stabilizers, plate, switches, and buy someone's stock Filco (or something) keycaps), you could probably come in around the same as a Filco. Make a cardboard case for it and there you have it. Otherwise, plan to spend serious money on this project.