Not only does the cost of 4 "C" range tires seem very high and even a lot higher than the 4 new Michelins "C's" quote as installed that are going on my wife's Trailblazer in about a week, the HO alternator and idler pulley cost numbers are insanely high. The book says a total of .7 hours time for both done individaully. Should be less time if done at the same time.
OP, you're being ripped off! Get more quotes and do the alternator/pulley work yourself if you can and the cost will be under $200 including fuel to go get to parts and bring the old alternator back for the core charge credit. Work should take less than a hour of your time and save you over $400. $400/hr is wonderful pay and no income taxes etc to pay out of it. You can do a lot better on the tire costs if you want to. You'll likely save $500+ doing the needed repairs and 4 "C" tires if you desire to.