I just had mine done again, and to me it was worth the extra money.. I had an "experienced" mechanic do my first set (4.10s), and they were noisy. I had him open it up to check, and the pattern was dead on. Then when I went to do the supercharger, I went to 3.73's, bought FRPP and the motive kit, thinking the better gears would solve the noise problems, and the full install kit would replace ALL the bearings. I didn't notice a change in the noise, and after a few hundred miles I went on the highway, and they were so loud I thought the rear end was about to fall out. I had them tear into it again, and they told me it was all good, but they replaced the pinion bearing anyway, since I was concerned it had failed. It was even worse that second time.
The mechanic wasn't charging me for the labor after the first try, but he was charging me for more royal purple and the bearings and gasket and such since I brought all that to him rather than buy it through him. I didn't want to spend any more money, so I ended up shopping around.
I found a shop that guaranteed it would be quiet, and agreed to work on it for zero charge if it wasn't, regardless of how many tries it takes. They got it perfect on the first try.
Thing is, I hear this kind of story over and over both in person and on the forums. The mechanic that did mine originally has done hundreds of rear ends, and probably just didn't realize that the 8.8 is particularly testy. If it isn't done just right, you get noise.
I applaud your courage in doing the install yourself, and am happy to hear it is quiet. The question I have is, if it had turned out to be just a tiny bit off and noise was present, would you still feel that $400 is too much?
For me, spending $800 for parts and labor, knowing that it was going to be right with NO exceptions was totally worth it. Granted it took longer than it should have because they first ran a pattern, then carefully dissected the rear end trying to discover what all was done wrong, but in the end, I got what I wanted - a quiet rear end. After almost 2 years of fighting a noisy set of gears, the money was well spent.
I guess what I am saying is, it is great to do the work yourself and save yourself money, right up to the point where something isn't right and your lack of knowledge or expertise prevents you from figuring it out and fixing it. At that point, the extra labor all of a sudden seems worth it. Just my 2 cents.
Sold: 2006 GT Premium Vert, 5 spd, Tungsten Grey
New toy: 2001 Porshe Boxster S