Usually you can just replace the mast assembly, around $35-40 from the dealer. This can be done from the top with no messing around in the fender well.

In a nutshell, remove the top nut, turn on the radio...old mast spits itself out. Install new mast lining up gears in the right direction, turn radio off...new mast sucks itself in..tighten top nut.

There are several threads with more detailed instructions around, here is one:

www.4x4wire.com