Good news time then....
If it only does it at sartup and a quick prod of the gas pedal sorts it then you don't have the failure yet. It tends to be more when it is warm and cruising from my experience. If you do need one then FCPGroton have them at a sensible price. You can then change it yourself in 1/2 an hour or so (without removing the inlet manifold which is how Volvo do it and charge 2 hours for) but then need to the the software updated before the car will run properly - a dealer job. At least you can cut the cost in half though! The part at FCPGroton is Genuine Volvo, FCP part ref 8644347 and costs $485... thats about half of what the whole job at a dealer would cost, but you still need the software update too.... Even so you should be able to get it done for under $650 if you change the part yourself.

Good luck!!!