500 is a bit steep, specially for someone without much experience. My going rate is 350 plus parts and oil per axle. 50 dollars extra if its some sort of actuated locker. ARB, OX, Electric. Axle in or out. One thing I used to do was I would provide an additional discount if they pulled the axle, and another if they came and helped. You could do that while getting started.
I've done gears for about 7 years, and have about 200 sets under my belt, so I'll provide some advice thats been a result of my experiences.
Always check the parts they bring over. Lots of folks get a deal on a box full of parts and bring you the wrong stuff.
Always keep extra ring gear bolts on hand. At least 1 full set. Jeep diffs except rubi's all use 3/8's so stop at the gear center and get a bag.
Build a setup inner pinion race for every diff you do. It will save time.
Keep as many spare bearings as you can on hand. You can sometimes get a bad pinion bearing out of the box. Choppy rotation when checking patterns is the first sign. Also, D30's have 3 variations of pinion bearings and its pretty common for someone to bring you the wrong kit.
Dont use a case spreader on jeep axles. Case spreaders can easily distort a diff permanently. Specially little jeep diffs. Use a dead blow instead.
Dont install beat up looking used lockers. Specially ARB's. They will come back to haunt you. Again, and again, and again.
Buy your oil, rags, and brakeclean in bulk. Shop supplies will nickle and dime you to death if you arent carefull.
Always pre oil when setting up.
Always have extra seals, crush sleeves, and pinion nuts on hand,
Always use permatex anaerobic sealant or equivelant on pinion seals. It only takes a few come backs before you learn that one.
Always set aside more time then you expect you will need.
Always get them to do a break in. 2 heat up and cool down cycles. 500k and drop the oil. We set stuff up tighter then factory, and aftermarket stuff has different tolerances. Silver flecks of brake in material is normal when they ask. As long as it isnt chunks, you're good.
If they want you to get parts, use northridge, he gives the best deals. Avoid the local shops here for the major stuff, as their prices are typically over double that of common U.S. prices.
A little tight on pinion preload is better then a little loose. So if you go over a bit, dont worry about it. But dont stay under.
A little deeper is better then a little shallow. Helical gears wear outwards to the end of the tooth. Lean to the deep side of center for the longest gear life.
8.8's almost never get a pattern on both sides. Dont kill yourself trying on the first one. Get the drive side as good as you can then bolt the POS back together.
Rule of thumb when going deeper on jeep axles is to swap over the stock pinion depth shim, add 10 thou behind setup race and go from there. Should be close every time, and only 1-2 more 5 thou adjustments from a finished pattern.
Good luck. If you ever have questions or are stumped on something, feel free to look me up.