But the need is still fundamentally inelastic. You're seriously ill from food poisoning and you've lost a lot of fluids. The ER nurse is about to stick an IV into you and wave your hand weakly and say "Wait, how much is that IV fluid you're putting in there?"
The nurse says $500.
Option 1) You say "no way, I can't pay that." The nurse shrugs and says "well, that's what it costs for IV solution here."
Option 2) You say "holy hell that seem expensive for a bag of salt water." The nurse shrugs and says "well, that's what it costs for IV solution here."
Option 3) You say "I'm really not comfortable paying that. What other treatment can I get?" The nurse shrugs and says "sir, this is the standard protocol for treating acute food poisoning. We put a saline solution into your arm via IV to replace your fluids. There is no alternate treatment. We're really busy in the ER, so I need to put this needle in your arm or get to another patient."
Now let's add a functioning market as you allude to:
Option 3, redux) You say "I'm really not comfortable paying that. What other treatment can I get?" The nurse says "well, we also have this other saline solution for a buck." You, reasonably, say "wait, what? Why is this other one 500 times cheaper than the first one?" The nurse shrugs and says "no idea, I don't make them. They both seem fine to me though." You, still being reasonable, say "then why is one so much more expensive than the other? Will the cheaper one do just as good a job as the expensive one?" The nurse shrugs her shoulders and says "look, I can't promise anything one way or the other. We default to the more expensive one but if you want the cheaper one, that's your choice. It's probably fine. Just sign this form that you're opting for the cheaper solution."
What does a rational person with zero context choose?