I feel that most labor costs from motorcycle mechanics to auto mechanics are a rip off to some degree. They generally charge according to what some book says the job should take as far as time goes. If the book says the job will take 3 hours then even if they finish in 2 hours, they charge for 3 hours. I recently had a front tire installed on my motorcycle and the dealerships service dept had a sign saying that labor cost $50.00 per hour and there was a one hour minimum.
I don't know how long it takes an ATV mechanic to change out those seals and bearings, but I wonder why it needs all of that? Were you experiencing problems with the quad? Since you were just looking for a brake job, do you believe the bearings and seals are shot? Do you ride in alot of water and or mud? How old is your ATV? Those things do wear out, but if bearings are shot then it seems to me that you would have experienced something (sound, or something) to indicate that there was a problem.