Rear End Rebuild..too much?

Yeah, that seems a little steep, shop around

Yeah, if you have to provide the parts that seems too high. Most shops here in Central Florida get 175-225 for the labor. Of course, there are at least three shops here in town that specialize in Mustangs so you have the competition factor, but I'd suggest calling around. There's nothing wrong with paying a little more for skilled (experienced) labor but you don't want to be paying for his time to "figure it out". If you have to take it to that particular shop to insure it gets done right, fine, but make sure they have lots of experience doing ring and pinion installs, not just lots of experience.

Also if he doesn't sell you any parts I don't think he's supposed to be charging you tax on his labor. Here in Florida you only charge sales tax on labor if it is on the same ticket (job) as parts.

Going rate is usually around $200, $400 if they supply parts. That's a little generic but that's what you can expect.

For that price might as well let the local FORD dealership do it!