The compressor is probably $500-$600 I’m guessing. 6lbs of R134A refrigerant (I just recharged my system and that’s how much it takes) is around $200. Labor at between $150-$200 an hour is 4 hours. I would say it sounds like the price is in the ball park!
I would not use aftermarket parts. I’ve seen them fail after a year. Stick with OEM for something like this. If you buy cheap or want cheap, you are going to get cheap, and you won’t like cheap when it fails a year later! I can promise you, you don’t want the $50 an hour shop working on any vehicle that needs to be reliable.