Relatively inexpensive - you can custome design a keypad and have them made, just like you get PCBs made. What an idea for a control panel - and not just the switches, they can embed LEDs in them! The main cost is the tooling, but that’s a one time charge, they actual keypads are pretty cheap. So the idea would be to deisng a puzzle piece sort of thing and have dozens made, then fit them together as needed. It doesn;t make a whole lot of senst to say draw up your whole ayrd and make one big membrane keypad - that would cost a fortune.
This video from Dave Jones talks about it and mentions one such manufacturer that he has used.
https://www.youtube.com/watch?v=H8XBBfvsPj0
–Randy