Figuring out how much a hospital will charge you for your medical care is insanely difficult — way harder than, for example, finding out how much the same hospital charges for parking. That lack of transparency in health prices partially explains why there is huge variation in what doctors charge for the exact same service. An appendectomy can cost anywhere between $15,000 and $186,000. Doctors don't usually feel the need to make their prices competitive when shoppers can't see them. Over the past two years the Blue Cross and Blue Shield health plans have been running a quiet experiment, to see what would happen if prices became available in some cities but not others.