How much can i expect to pay to get my 2007 milan door fixed?

We have a 2007 mercury milan. Yesterday one of my rear doors started acting up. It will not lock or unlock using either the "clicker" or the lock/unlock button in the front. I will only lock or unlock if I manually unlock/lock that door. All other doors work fine. Also the motor works, you can hear it running (longer than usual) and makes a funny noise. Could something be knocked off track??? How much could i expect to pay to get it fixed? Would i be better off taking it to carmax (where we bought it) the mercury dealership or a little "mr fix it" shop. Thanks.