Actually I found an interesting video how to make the prints on keycaps yourself:
So making your own keycaps might be time consumpting, but not to hard to do yourself. Many copyshops have printers with dyesub ink, if they offer printing on cups or other materials. So you do not actually might not need to buy the dysub ink and an inkjet printer with piezo printhead to print on dysub transfer paper; you might let print it in a copyshop...
So all you need is blank keycaps in the correct size (esp. the 10 function keys).
Exept for early A2000 (with cherry switches) all original Amiga keycaps are pad printed - the lowest quality of making keycaps (even on the early A2000 the Amiga keys are pad-printed). Laser etched and dye sub are both higher quality, with dye sub even allows multiple colours. They are only topped by double shots (only used on the early A2000 exept for the Amiga keys).
Also you do not need a pcb. Good Cherry Keyboards use a metal plate to hold the switches anyway. Of course you can make such metal plate yourself using an aluminum plate and a Drehmel or Proxon tool, so no need for a PCB for mechanicly hold the switches in place. Maybe it is even enough to 3d-design and print such a plate and support it by some metal. You simply use wires to connect the keys some way as on the original a500 membrane and connect the wires to the existing a500 keyboard controller.
I replaced the membrane of a keyboard by individual switches and free wired them to original controller about 30 years ago. It was not an Amiga and I had more space in hight available, so I was able to simply glued the switches below the original keys, so I neither had to make a holding-plate nor new keycaps.