Car Talk listeners recommend RepairPal for Android and iPhone to help you get a rough estimate of how much a given repair should cost based on the type of car, and your location. The app also points you towards repair shops, as well.
What Car Talk visitors say:
"When I was driving to Portland with my lovely wife, we broke down in a remote part of Oregon. Fortunately I had the app and we were able to get towed to a great mechanic nearby even though we didn't know the area. Now I use the app whenever I go to the shop, and have avoided paying a few really outrageous quotes. In all cases the mechanic brought his price in line with RepairPal's quoted price." ... Chesshcat