It sounds like you ride your current bike and it needs service and parts which is extremely common and something you should do regularly. $120 for all of that stuff is a little on the lower end with labor without labor it in the lower range still but not uncommon though I would recommend replacing chain and cassette at the same time and certainly Swiss Stop or Kool Stop brake pads and good tires for commuting like say a variant of the Schwalbe Marathons (there are a bunch).

I would also get a new bike as well. More bikes are better but in the case of a commuter 2 bikes are the real minimum if you are daily commuting by bike and don't really stop. I have for years gotten the people who absolutely freak out when they need their bike serviced (which was usually years ago) and can't leave it because the 20 other ways to get to work are unknown to them or so foreign in nature they couldn't understand them yet they only have a single bike. Having that second bike means one can be in the shop getting worked while you ride the other and swap out as need be or one is a rain bike and one is a good weather bike and still the same sort of concept. Plus having a different bike means a whole lot of things.

I have lots of different bikes for different purposes and I think save for one bike I have commuted on all of them at least once usually to do work on them or because I had a ride in the evening or the next day at work or something.