AC compressor “coming apart”

A/c repairs are one of the most expensive jobs to do. Time, labor, etc. I would have someone else do an estimate or if you know someone willing to do the work you trust have the garage evacuate the system and have you or your friend do the work such as replacing the compressor, receiver drier, and condenser and refill. To answer your question whether that is within reason for the estimate? Perhaps depending on what exactly is being replaced or not. I think you could do better on the price if you shop around but just make sure you compare apples to apples concerning what parts are going into the mix. Good Luck!