Toyota Sienna - New AC Compressor Needed?

My wife's mini van has been having some AC issues. Mechanic we took it to said it needs a new compressor and quoted $1600 to replace it. Also said it could need a new expansion block, which they quoted $1200 for. Digging in a bit, if expansion block means expansion valve, that looks pretty high. I wanted to get additional opinions on this and also consider the possibility of replacing the compressor myself and taking it somewhere to get the freon recharged.

Here's the details:

• 2013 Toyota Sienna
• AC does not blow cold when the car is sitting still. Once moving, it does blow cold, but not as cold as it should/used to.
• We had freon checked. It was a little low. I think it calls for 2.3 pounds and we had 2.1. They put it to the recommended level and it did not help.
• Mechanic stated he put gauges on the compressor and is not seeing the correct differential. I have a gauge set from a mini split install and could recheck this myself.

Questions:

• Do the symptoms described sound like a compressor problem?
• Is $1600 to replace reasonable?
• I'm handy and mechanically inclined. I've installed a couple of home mini splits. But I haven't done a ton of work on cars, and none on auto A/Cs. How hard is a compressor replacement? I'd prefer not to take the $1600 hit, but I also don't want to get in over my head.
• Am I missing something with the "expansion block?" I was talking to the receptionist, maybe she meant evaporator coils? That would make sense to be $1200.

Thanks for any input