Last time I check best buy charged $130 for os install but I bet that price went up with vista.
I dont have a set rate myself, i charge by the hour - and when i click install and i sit and wait for 45 minutes, i dont charge because i either work on another computer or watch tv. The difference is that when you go to someone's house, you are infact just sitting there and I cant get any other work done.
Some places charge $80 an hour so if you spend 2 hours installing windows and getting windows updates plus the cost of driving to their house, not to mention that guy who went plus his manager both wants to get paid - that is hwy it is so high.
I work alone, trivel to location for free, and charge less than $80 per hour so my customers are always happy. I keep track of my customers and give them forms to fill out about me - I asked them to rate various things about myself and they give me 100% for customer service and 97% ffor the end result.

97% is really low, I have to work on that.