Not sure on the price of the BCM. I've never had to change one.
Here is the GP door lock circuit
http://img96.imageshack.us/img96/527...rdoorlocks.jpg
See how the door lock switch circuit is independant from the door motor actuator circuit? The BCM controlls the door lock actuators.
You could have a bad BCM or Keyless entry receiver.
Have you tried reprogramming your remotes via removing the MALL PGM fuse? I'll see if I can find those instructions.