V70 T5 Rattle on start up

[wisemen]

Guys, V70 T5, 2001, last few days engine has made a sound like a bag of spanners has been chucked into the engine when first starting up and again when air con is on.

I've had my local garage collect this morning and they have advised me its the air con compressor / pump that has given up the ghost!
A quick look and they appear to be around £350 quid for a replacement, plus fitting, garage has quoted me £500 all in. They advised that they can disconnect and everything will still be OK, just no cold air. I'm fine with this but is this correct? Will everything else be OK with this simply disconnected?

If not, has anyone any ideas on where to get a second hand item? I don't fancy shelling out £500 on a car that's worth £1k tops.

Any help much appreciated.