Probably at least $15 per faucet and valve material cost. You are paying for a service call and the installers time, so that's probably pretty decent price. May not seem like it when you see how easy it is, but you are paying for what he knows, not what he does. I would imagine his hourly rate to be around $75 per hour. Unless he owns the company, he isn't getting all that money. The boss is paying for the vehicle, insurances and fuel, plus the cost of maintaining his tools.
If you have never made a mistake, you haven't done much.