If I hired someone to fix my plumbing and they wouldn't give me an estimate and then decided to charge me $20k/hr I don't think a court would honor that contract.
Whoever has the most money in America captured the regulators and politicians through money conveyed to them by lobbyists.
You live without plumbing by making different arrangements but you can't live with a fatal lyssavirus.
To me it just seems like fraud. Forget about patient choice because in this situation the patients conceivably could have shopped around for rabies shots, AFAIK you aren't going to die because you got your rabies shot a few hours later the you needed to. The problem seems to be that even if they were able to shop around and find the lowest price apparently the hospital can just charge whatever they want regardless of the expected or quoted cost.
Going back to the example of the plumber; Imagine if my house is flooding and I get into contact with two plumbers, one tries to price gouge me and quotes me $5k/hr and one is seemingly honest and quotes me $80/hr. I go with the plumber that quotes me less but then he ends up charging me $50k for the teflon tape he used anyways. We can see this isn't a breakdown in being able to shop the market and the normal competitive dynamics that arise from that, the breakdown occurs because of the fraud.