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I have looked into it for awhile. The actual physical part of purchasing switches and key caps is easy and relativey cheap. The transistors are readily available and the solid copper wire cheap. I have a workshop with the equipment,mats and the experience to build a nice box/platform. Yesterday looked into the Coding Installation that looks actually pretty easy. You can DL a Keyboard software install and customize it to your liking without really getting into actually writing code. The PC electronics piece is priced just over $20 for a 5 volt version and has like 48 pins available. For my Custom Claw I counted a requirement of only 28 pins.I gave up on the idea myself, but look forward to your results!
I build RC Sailboats and have some commitments in that regard at the moment so it may be a few weeks before I jump into this but I can imagine a weeks worth of work and less than $100 USD. Sure I will send a few pics.