Ford Repair: 4 wheel drive, vacuum line, shift on the fly

Question
I have a 2002 f350 and the 4 wheel drive quit working. A guy told me that it was the gem neck went bad and said that it needed to go to a ford dealer for the part and to be re programmed. How much money am i looking at to get it fixed.

Answer
if it's actuallt the gem that went bad, your looking at 1000.oo plus to get it done. there are mutiple other possibilities though- if it's shift on the fly 4 wheel, it could be as simple as a broken vacuum line or a bad seak internal to either the left or right hub. or just the actuator on the fender well.. did this happen all of a sudden ?