Comment by JaggedNZ

I spent a number of hours building a minidexed from a RPi Zero 2 and parts I already had on hand, and it still doesn't have a proper case. Add 40 buttons, 8 pots and a screen, that's an easy $20-40 worth of parts. Then there's lithium battery and charging curcuits.

Or just buy an FM-1 for $60, most musicians are not hardware hackers.

For the hardware hackers there are hundreds if not thousands of open-source projects. Infinite Digits Zeptocore immediately comes to my mind.