What % of medical expenditures does this scenario encompass?

You're describing a corner case that can be, at least partially, planned for ahead of time (by consumers, insurers, a combination of the two, etc).

And sometimes your hand is forced in all sorts of markets. But if enough shoppers are even somewhat price-discerning, the "value per price" that you pay for a given good or service should be significantly lower than it is in the current state of affairs.

Emergency care (and EOL) represent the majority of all costs for many people. Other than regular check-ups I haven't been to the doctor more than 30 times in the last 30 years. One visit to the emergency room in an ambulance is at least $10k and that is equal to 30 years of $300 visits. A real emergency can easily be several $100k once you figure in recovery. So I can't shop at all for 50-90% of all my spending!

After a heart-attack/car-wreck the ambulance should take me to the closest hospital not the one that happens to be 30 miles farther away and in-network. If I'm EOL care, then I likely have pre-existing conditions and travel limitation that will limit my ability to change plans, much less hospitals.

You want added irony? Insurance has been known to deny ambulance bills because the ride "was not pre approved".

Including Heli EMS from car accident scenes...

How do you shop for life insurance if you are dead?