Mass-produced ergonomic keyboards are around $400 USD these days. The more of it you build yourself, the cheaper. I can build one for some $15, having already sunk the costs of a 3D printer, soldering station, some switches, some keycaps, a few Pro Micro boards, and lots of time learning about it.

But before my wrists started hurting, I never went for expensive nor weird keyboards. An IBM Model M passed into my life a long time ago, and quietly back out of it after only a few years, relatively unappreciated… Crazy, I know!

Geekhack is indeed a good forum! Deskthority.net is another.

modelfkeyboards.com is a thing, too. (I’m not a customer, nor associated with them.)

I’m all in on MX-style keyswitches, because you can make keywell keyboards such as the Dactyl Manuform with them. See for example !ergomechkeyboards@lemmy.world. Keywell keyboard design and manufacturing is… shall we say, much more decentralized than Model M keyboard design and manufacturing? :) Many people can make you a curvy keyboard, and there are many varieties, or you can make one yourself, and customize its form as you wish. But this is all far afield from what you actually want, I’m afraid.

Your question also brings to mind beamspring switches such as https://kono.store/blogs/keyboards/silo-beam. Similarly that does not appear to lead to the same kind of experience of clicking a button, paying your money, and getting a pre-existing keyboard removed from a warehouse shelf and shipped to you in a few days, as you would get with Unicomp.