The ATM has generic Logitech camera for scanning QR-codes and very common bill acceptor called MEI.
The camera is USB, while MEI bill acceptor is RS232 connected.
I will try to use USB-RS232 convertor to get everything on USB.
It's probably easier to go get a working USB bill acceptor.
Just my view, but if you do have issues then it's just another thing to diagnose. Is it the acceptor, is it the usb <-> serial adapter is it something else to go wrong.
I don't know your budget and yes a $25 usb to serial is a lot less then $300 for a new acceptor but it just might be worth it. Not to mention you can still sell the old one.
I don't know where you are so I am just using US prices, if you are someplace else in the world I could be totally off.
-Dave