If money is more important, buy the cable first and see if that takes care of the problem; it needs to be replaced anyhow based upon your description. Next focus on the encoder for the motor.
For the type of parts you will need for this repair, just buy the parts from your dealer. You probably won't beat their prices even if you do find them somewhere else. If they don't have them in stock, they are always available next day air.
Good luck! Report back what you find.