Ford is too over priced. And yea, 1500 wouldn't surprise me. I myself am an apprentice working at the local ford dealership, and although they haven't started me on doing diffs yet, I have heard some scary numbers come from just replacing the rear end clutch packs on the new half tonnes all within the hour and a half it takes me to do them.
personally, I would look to a reputable gear center with a decent rate. When I did the d28 in my ranger, I had sourced all of my own parts and did it myself.
The majority of the costs I hear about at work, quite often gives me the chills. And on another note, and depending on how old your rear end is, ford may not even be able to get anything. Usually they can piece a package together with whatever they can find, but allot of the time ford doesn't supply formal kits period. So my dealership often looks to the gear center in red deer for kits and gears.
good luck.