2009 Toyota Highlander, 140K, been running great and blowing cold air. For the past couple of months I've been hearing this squealing, grumbling, type of sound from the pulley side of the engine. It only is present at idle and when the A/C is on, if I'm idiling with no A/C the sound is not present. I know it can be a lot of different things and how the A/C being turned on puts a lot of strain on the engine pulley system. A mechanic is gonna look at it later this week, I told him what i'm telling you, and he said most likely it is a bad compressor but will check it all out. My question is if he finds it needs a new compressor what is reasonable full price for this service, parts + labor?

Thanks!