2007 Mercedes Benz C230 altenator

For original warranties, it depends on the level of warranty. Usually for the first year or two on a new car it would be covered, but after that, only if you have the premium extended warranties.
For aftermarket and used vehicle warranties, most basic ones won't cover electrical components like the alternator. The upgraded ones usually will though. Best to ask the warranter or read your warranty details.

Labor for replacing both front brake pads should be about 1 hour which is equal to about $80 - 100 depending on the shop. You can price the parts yourself depending on which brand and store you choose will make a big swing in pricing.

If you let a shop charge you 800 bucks to replace front rotors on your car thats your own fault, there is nothing special about replacing rotors on this merc than any other vehicle and it only takes about 1 1/2 labor hours to do so..unless they are charging you over $400 an hour than there is no way it will cost that much. I even found new rotors at $100 each, so even including 2 new front rotors and labor shouldnt be more than $400...