Alternator replacement

[MosH]

So I have owned my X5 for a little over a month now. Its a '03 purchased from the orginal owner with 37K miles. Yesterday the battery light came on out of nowhere so I went home and did a voltage check. Low and behold I have 11.9V when running so no putput from alternator. I called around and found a reman for 145 locally and then decided to call the shop the previous owner used for any work in the past. The quoted me 325 total parts and labor to replace with a reman 120amp bosch unit. I took it there this morning, for 180 more then my cost I didnt feel like chopping up my large hands trying to wiggle it out. Does this price seem fair? I am reading about battery light issues people are seeing, I am thinking I should replace the battery right away when I get the car back today since its the original battery but apparently its still very strong since I drove for 45mins with battery light on running on just battery and no alternator. What is the best battery available out there? Interstate? Duralast?

I have to say I am a bit surprised the altnernator has gone bad at 37K miles, so is the mechanic, he will test what he can before replacing the unit today however I am not getting my hopes up. I hope this is not the start to electrical gremlins in this truck.