I paid $140 to have 6 pounds removed from a PSAIII (went from 58 to 52# @ 28"). Mine might have been a bit more because I had a "motto" added under my already present name. This price included return shipping. I thought it was a bit expensive but it saved the bow, for me at least. That bow was headed for the block because it was hotter than I care to shoot these days. I am very glad I did it. I can't tell a bit of difference in the bow's appearance because it was as new before and after. It took about 3 weeks because I caught them (end of July I recall) during a down time.
I don't know how they do it though. I figure they jog with it, put it on a treadmill, rub it with grape fruit...