ER's are different animals from the rest of the hospital.
I pay dearly for my daughter's Blue Cross Blue Shield cash policy, and she had to go to the Emergency Room a number of times--$300 deductible. It galls me to see people in there on Medicaid walking out paying nothing. Then I see them at Walgreens paying nothing for prescriptions when I'm paying $50 or $100 for the prescription for my daughter.
And a couple of weeks later, I'll get a $400 bill from the Emergency Room Physician who doesn't even work for the hospital. That's for 3 minutes' contact. And he's not a BCBS authorized provider. It's like he works for whatever he can get out of insurance companies and individuals.
So the ER bill is not the only bill. You've got to deal with the ER physician, and his billing service will charge off the bill if unpaid. And they report the charge off to the Credit Bureaus at the same time they sell the note to a collection agency.