He was talking about the TIPM (Totally Integrated Power Module), and it directly controls the power to the door lock motor. If it works sometimes I doubt it's the module, but it is possible, and yes, they are expensive!
First thing I would check is the ground connection behind the kick panel on the drivers side (by the park brake). Behind it are 2 ground points. One low and close to the door and easy to get at....that's not the one you want. Your after the one that's a little higher up and toward the firewall. You may have to change the position of the park brake pedal to get at it. make sure it's 'Tight'. Doesn't hurt to remove it, clean the connector(s) and re-attach.
If you still have an issue, reset the whole system before proceeding, just to make sure the computer(s) are not just acting stupid. Then open the door panel and check the connector on the lock motor. Sometimes just removing at re-connecting (cycles contacts) is enough to fix the issue. While you have the door apart, it is also a good time to check the condition of the wires between the door and the B pillar. Your specifically interested in the 2 Tan wires. One has an Orange stripe, the other has a Violet stripe. These 2 wires have opposite power depending on whether it's asking for lock or unlock. These are the actual motor power wires. Hooking up a voltmeter between these 2 wires will show about 12V for lock/unlock and -12v for the other. If the power is good, then you can be somewhat confident that a new motor will fix the issue......assuming no mechanical issues are binding the mechanism.