Have fun
FWIW it occurred to me that my "cheap and easy" paper clips+foil idea might well end up more work and more expensive than Eric's scrap bronze strip idea, even if there were no other problems. Not that I've worked it out properly, just speculating.
Also I think the polarity of my version would be opposite (switch would be
on when the card is in) and would probably need a little transistor inverter or such to get the same behaviour.
Each of those might be only about 5p or equivalent (10c?) but might end up a lot of soldering if you've 50 of them. Not sure how any of this might fit in with Eric's matrix suggestion though, got a headache this morning so I can't think clear. Maybe matrices suffer from collisions(?) though, if you expect to have multiple cards out at once.
One medium-tech answer to the lots-of-wires problem (for either switch type) if PICs are out of the question: maybe a couple of shift registers, a clock generator and some other logic chips might make a workable multiplexer to get a collision-free representation of the cards over 2 or 3 lines. No I don't have a design for such a thing ATM XD And yeah, digital circuits might be a PITA to work with
Meanwhile, I realise I don't entirely understand what the situation is with this, I think I missed some earlier thread: is it that you've got one booth where people order stuff and get given the cards from the switchboard, and another somewhere further on where they bring the cards to to
collect their order ("fryer's booth"? Food?) from you?
If so, just how far apart are these booths? Perhaps there could be an even simpler approach. And is it necessary here to get the cards
back to the ordering booth? Or switch off the indicators for an order you've got ready which hasn't been collected yet (so they don't distract you)? Any possibility of an overstretched booth attendant putting a card back in the wrong slot?