'91 passenger-side door lock problem

I have a '91 Eddie Bauer. The passenger-side door lock doesn't lock/unlock using the buttons on either the driver/passenger panel. It's the only lock that does this. The panel on the passenger side does lock/unlock all the other doors fine though. Also, when I lock/unlock the passenger side from the outside, the key has to be turned the opposite way of the driver's side door! Not sure if this is because of previous owner's tinkering w/ the electrical system or what. If I have to remove the inside panel, what would I be looking for, how much would it cost, etc? Thanks in advance!