i typically charge 400 labor per axle. which included all shop supplies and oil
500 if other annoying factors.
your IFS ish thing might be annoying to pull. it might even been a clam shell diff thats not a conventional style diff i dont know. i stick to mostly straight axles and jeeps. done a few big things which are the same just heavy.
im not up on GM costs, but new JKs is about 600$ total parts for everything in 2 diffs (yukon gears, Timken bearings and master install kits)
in short, i would say the labor cost is not off far, but i would research parts cost, and ask what kind of gears / what kind of bearings are they quoting and check on that your self.