Back in 1978, I made my own keyboard for a single board 6800 computer I designed, also because I could not afford a keyboard.
I went to a surplus store and bought an EBCDIC keyboard for a couple bucks. I unsoldered all the keys from the circuit board. I took a plastic board, and using the old circuit board, drilled holes in it. Inserted the keys in the holes, and then wired it up in an 8x8 grid pattern. The two 8 bits gave 64 possible keys, which was enough, connecting those to an I/O port enabled recognizing which key was down.
It worked fine as long as you were careful not to press more than one key at a time.
I don't recall what I did with that computer. It's all gone, including the design notebook for it.
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