Checking the lock mechanism and central locking servo on the pre facelift are easy its just a case of removing the door card and then access is plenty.
Not really worth spending out to have a garage rip you off imo when it can be done DIY style saving the labour costs.
The pre facelift door cards are pretty straight forward to remove once off its a case of disconnecting the rod from the inside handle the door button remove the motor, which from memory is held in by 2 screws and then it just unhooks and then remove the Lock mechanism cover its just clipped in place then when you lower the lock mechanism itself which is held in pace by 3 star screws on the door edge, the outside door handle bar comes away, then remove the lock mechanism from the door.
The above free's up the lock for repairs if needed, I found mine seemed to be jamming and was in need of some wd40 the CL motor have a tendancy of snapping inside the rubber sleeve but it sounds as though yours is ok.
HTH