1 DIY would cost you less than 100 because you can buy a remanufactured alternator from Autozone or other parts store.
2 If you can't DIY, you should go to an independent shopt. they are usually much cheaper than a dealership.
However, A bad AC compressor or water pump would cost you more. So you can take the comfort that the dealer didn't take the most expensive repair.
The money is already spent so don't cry over spilled milk, cheer up and enjoy the Christmas.