While I can sympathize with the cost factor, go to the Atlas or Lionel websites and look at the exploded diagrams for a GP-30, 35, or 60 for example. Or the SD-40 or SD40T-2. These are nightmares to disassemble if a wire breaks between a pickup roller and motor, or try to stuff the harnesses back in and get the shell back on properly. Maybe postwar repros, but I think the savings there would be negligible.
Terry