If you have the used part in hand, I would take a shot at replacing it yourself. The brake systems on these cars are not very hard to work on. The hardest part is probably just bleeding the sytem afterward, and thats a piece of cake. Just get a decent shop manual, a good set of tools, and a big bottle of DOT4 (which you said you already bought). Also, make sure you use penetrating oil on the bleeder screws on the calipers before trying to open them. If they are stuck and you use to much torque trying to open them you will snap them off, or strip them. If the screw strips you can try and get it out with a set of vise grips and then just get a new screw, but if the screw snaps off in the caliper you'll have to throw it away and get a new one.

If your still looking for a decent shop, my friend Dan is a Volvo/Saab/Jaguar specialist.

Coventry Import Auto, Bridegwater NJ (Somerset county)

I've also used J&L Car Clinic in Red Bank. They did my rear main seal and did an excellent job, prices were very reasonable as well. He used to be a master tech at Bridgewater Volvo before opening his own shop. Don't know his policy on using used parts though.