prices depend on where you go, who does it, if you know anyone, so the price varies on install.
some places want you to drive in, drive out, all their parts, that way they can warranty the work better. Don't pay extra for an 'extended warranty'. Waste of money.
I've gotten quotes for $350-500 per axle, considerably more for the front but i know you don't have to deal with that.
You really should just call around and see what shops say. I'd do quality gears like Yukons and a master install kit(bearings, races, shims, etc) and replace all the seals while they're at it.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.