Door mechanisms don't work on both rear doors.

Door mechanisms don't work on both rear doors. I have an 2001 Ford F150 XLT with the extended cab, not the model with full size rear doors, but the smaller half door. Both of the door mechanisms don't work anymore. I would like to fix them but don't want to pay what the dealer is asking for the replacements ($165 +/-). Any suggestions would be greatly appreciated.