The fix should be relatively easy. Open up the driver door, and check the electrical connections (loose connector,voltage line) to the door actuator. If the electrical connector seems ok, and the actuator still not working, take the actuator out, and test it individually. If it still don't work, then you will need a new actuator.
Different shops charge different price. Take it to a shop that you can trust, if you don't know which shop to go, the best bet is go to your car's brand dealership.