Even if there were perfect competition, it doesn't matter much, people don't comparison shop for ERs. If you are having a heart attack, you're not in a position to compare prices at local hospitals.
There was a similar thread a few weeks back:
https://news.ycombinator.com/item?id=6258597
It'd be great if the HN community started throwing out some ideas for disrupting this behemoth.
Good luck with the same at hospitals though...