You can get really cheap boards on taobao, for sofle, lily58, corne(all 3 are open source/open hardware) keyboards. You can of course also get prebuilt ones with or without switches for cheap if you want to. But in today's world, if you have tools and access to a 3d printer you can get a board for a few bucks some components and finish the whole thing with good switches and keycaps for 20-30 dollars.
It's a fun experience, and a nice reason to play around with SMD soldering techniques. I had my daughter (4 years) solder the hotswap sockets.
Worth checking out the miryoku layout, which is optimized for small keyboards, where I recently added sensor bindings for ec11 encoders[1].
