[defterGoose]

To piggyback on this: I've disassembled a 2nd gen Axiom 25 for research purposes. It's a pretty industry standard entry-level semi-weighted keyboard with decent controller capability. The keyboard and other buttons are implemented with custom large-format FSRs and several-shot molded (silicone?) membranes/switches. So you get physical feedback from a combination of a spring on the key root and the squishiness/variable force of the silicone contact. None of this is cheap, but it's not impossible to prototype either. It's just a very high bar.

Edit: I was particularly impressed by the engineering of the drum pads.