I've just completed a keyboard inspired by the Lisp machine keyboards but aimed toward use on a modern Unix system. Making your own one-off hand-wired keyboard is time consuming but pretty easy if you can solder. I probably spent $400 all told, including a fully custom keycap set from https://fkcaps.com/custom/

I've been meaning to write a blog post about it but I'm still finishing shakedown (currently chasing a wiring problem that messes up multi-key chords on the homerow)