Holy ish!!!!!!!!! You're getting taken. It's not a fun job but it isn't worth $800!!!!!! If the alt. is $200 alone then he is charging you for 8.5 hrs. labor at $70 an hour! I doubt book time is more than 3 hrs. for a mechanic. I would think 400-500 with parts included. Follow the how to and do it yourself.
At $80 an hr x 3 is $240 for labor and another $200 for the alt. $450 is reasonable to me.