1. Doctors overprescribe because they are afraid of mistakenly underprescribing (we are a litigious country after all). This end up costing patients more tests/procedures, and cost doctors malpractice insurance premiums. 2. Procedures are billed differently per insurance policy. There are millions of variations of anthem PPO, and what they cover and how much they pay differs.
3. You, as the policy beneficiary, only care about your out of pocket cost. You don't really care about the price unless 1) you pay some percent of the money (reference pricing), 2) you are below your deductible.
So you are right, price transparency alone is not enough, but it is indeed a big step. If you knew in advance the price of thing, you probably wouldn't pay 400$ for a bag of saline solution [1]
[1] http://www.nytimes.com/2013/08/27/health/exploring-salines-s...