I need a pendant for EMC. Since Mach2 is based on EMC, I guess it would be very little if any difference.
The electronics can be made a number of different ways. Some was already mentioned. If using the old PS2 keyboard interface, the protocol is simple and well known, so a microcontroller can easily use that. USB is not that easy.
But the membrane keypads are very expensive in low volume. I know because I use them in a design I made at work. They have a very steep price curve that doesn't level out until you're ordering them in thousand(s). So if there is a cheap mass produced product that has a suitable keypad, that would be nice to know. To us it may be more worth dead than alive!
So keep your eyes open, and keep on posting any links. Of course international availability is desired here, as we are all over the world, and freight cost often prohibits sending items like this.
The $5 cost price for a PCB is not too far off for a professional quality board in qty. >100 and a couple of weeks lead time, as the size is small. A pool board may come at that price, but you loose some quality. Again, what about freight costs? Bulk shipments to "distributors" in Aus, Asia, Africa, Eur, USA?