Welcome to Geekhack!
I wouldn't really know where to start.
Do you want to build a keyboard? Or buy one ready made?
Are you interested in cheap but reliable older (some might say "vintage") keyboards? Or a newer keyboard?
Something with a standard layout? Or a bit more exotic?
A full size keyboard? A TKL keyboard (with the numpad)? Or a 60% keyboard, perhaps, without function keys or a numpad? Or even a 40% (which omits the number keys too)?
There are so many choices.
Depending on where you are, something like a non-backlit US ANSI TKL keyboard with Cherry MX switches would probably be a good place to start with a minimal modern keyboard.
If you want something a bit older, you could look for a Model M (or an SSK, which is the TKL version albeit usually somewhat more expensive), or perhaps something with Alps switches.
Either way keyboards are available for under $100. The CoolerMaster QFR, for example, is often $80 or so, and a reasonable Model M can be had for about the same (but might need a little work to clean it up, and they almost always clean up very well).