Oh, don't pile more work on Lowpoly; let him grieve.
I think most, if not all of how to make a keyboard is documented on this site. I made my own rough prototype with nothing more than laser cutter, acrylic, key switches, a commercial controller and soldering.
for casing, 3d printing is very expensive. you can probably CNC the casing because it's mostly flat. I'm not hung up on looks, so i'd just make a box out of acrylics screwed together.
of course, hand wiring is tedious and error prone. it's best to use a PCB board. keyboard PCB is too dense to be home made. PCB prototyping service isn't too bad actually. a single piece that size would be $500-$900 depending on the options. i think ordering 5 pcs would drop unit price to less than $200 per board. plus $25 - $100 controller. That's just my rough estimate.
switches, stablizers are available parts that would be about $1 a piece. that's about a couple of hundred. cheapest caps are just salvage ones, ripped from a commercial keyboard. if you want special caps, that would be expensive but can be ordered.
so if you make a single board with a PCB, you are looking at at least seven hundred dollars worth of stuff. probably more. About a top end iPad? I think a good keyboard is worth way more than an iPad. of course there's also hours and hours of labor, e.g. PCB design. any mistake you make would be costly. if you count that, having a one of a kind keyboard made would run a couple of thousand, and much more if you want it pretty.
if you hand wire like i did, you don't have to pay for the PCB and that'd probably end up being a few hundred plus lots of work.
If anyone is still interested, I can write up a demo. it's been a while since i made my last keyboard, which i used heavily everyday at work for 8 months. but I don't know exact detail of how to wire the pointing sticks.. no idea what the part number is. i got a few here i can try though. it has four connectors and i'm not sure how to wire them, and what driver to use. Anyone?