2008 Ford Explorer front differential

That is a very rare repair for a 2008 Explorer with 28,000 miles !

If you did need the front 4x4 differential replaced completely, I would say you would be well into the thousands !
Just to give you an example. Say it was the "DANA" front drive shaft. It would cost $1000.00 just for that part alone!
Plus $125.00 in labor.

New 4X4 differential
New associated parts if needed
Labor for dis-assembly and re-assembly.
B. I. G. $$$$$

Sorry for the bad news;

Maybe it is something else! What is going on with it?

Rick