I had the same thing done last summer. I believe my cost was around $1200. The job is a total rip off and volvo should be ashamed for putting such a fragile piece in a critical location. Anyway, your cost sounds good. There are really only two components to the throttle system; the throttle body and the foot pedal. the foot pedal is pretty much just a variable resistor and seems to be very reliable. the throttle body is very complex and consists of a servo motor that opens and closes the throttle plate in response to the engine computer. what happens is that the throttle is opened only by a signal from the foot pedal until the car reaches temperature where it is then controlled by the computer in closed loop mode. the computer needs a feedback signal from the throttle body and i believe it is this signal that fails. when it does the car stops. some posters have indicated that they can or know of vendors who can rebuild the throttle body and way less cost. installing a new body is not very difficult (about 1 hour though the volvo book says 4). the kicker is that the computer must be reprogrammed if the body is changed so you are stuck going to the dealer or a shop that has Vadis.

One thing you might want to check into is if your emissions parts are covered by a different warranty than the rest of the engine. If so, you might find that the throttle body might have a longer period.