First, find your insurance information, go on line, and read up on your coverage.
(For example, my son had a pre-planned, pre-approved surgery and my insurance company denied ALL coverage. After the pre-approval and referral. When I looked up my insurance coverage, my out-of-pocket costs for an outpatient surgery was supposed to be $125. So, we contacted the insurance company and the hospital did also and it was covered.)
In any event - most insurance has *some* ER coverage, though it may only be 50%. Check your coverage! Then call the hospital with the result, once you know the answer. Then, negotiate. Many hospitals have "hardship" funds also, you could ask about that. (Donations that cover people who cannot afford their treatment.)
Looking up the info online might be hard if you haven't ever created an account, but it's totally worth it!