Yeah, velocity definitely jumped out at me as a difference, but it seems(?) like being velocity-sensitive could 2x the cost, maybe even 3x, but not 10x ¯\_(ツ)_/¯

I'm absolutely not calling it over-priced, just puzzled.

Well the only moving part in a typing keyboards is a mass-produced switch that you slot into a PCB. There are mass-produced hall effect switches that can provide velocity sensitivity, but it's a pretty distant comparison. The keys on a lumatone aren't anything like buttons; they're weighted mechanical arms with significant travel -- much more like a piano key than a keyboard key. And it has 280 of these! The degree of mechanical hardware in this thing makes it seem not really comparable to a PCB with some switches slotted into it.

That said! There are people making DIY isomorphic keyboards using hall-effect keyboard switches. None are commercially available right now, but see e.g. the MidiHex at https://gullsonix.co.uk/. You could make one for a fraction of the cost of a lumatone -- but of course it would be a very different instrument.