Things become a bit more involved in the repair process if your camera is not of recent manufacture. Manufacturers often do not stock parts for their equipment after they are seven years out of production. This means you will often have to deal with an authorized repair center or an independent agent. One of the first things to determine is if the repair is economically feasible. Don't expect free estimates.
Diagnosis costs the repair center.
A decision needs to be made if you are throwing good money after bad. You may be able to replace the unit with a newer model or perhaps pick up a good used one for the amount you are going to spend on the repair. This may not always be an option depending upon the age of your piece and how integral it is to your system. Another point to consider if the repair will be expensive is that it might be time to bite the bullet and upgrade to a new system. I would find the big deciding factor to be whether you are currently using an autofocus system.