Re: serpentine belt replacement
From what I have seen, it is more typical for the tensioner pulley to freeze up and break the serpentine belt, but the alternator can do it also if the bearings seize. Usually, you will get a bit of noise first from the bearings going bad, but you may not be able to here it over the cooling fan. If they are using a Chrysler new alternator, the $500 is probably in the ball park. If they are using a generic rebuilt unit, I would say it is high, unless it is a very difficult one to install.
I would definitely want to see the alternator when they take it out, as it is fairly common for shops to try to sell alternators, water pumps, etc when they do a belt replacement.