As of Jan 1, 2022, US healthcare providers are required to provide good faith estimates, and the final bill can only be $400 more than the estimate:
https://www.hhs.gov/guidance/sites/default/files/hhs-guidanc...
https://www.hhs.gov/guidance/document/guidance-good-faith-es...
When I went for my annual wellness exam, the doctor's office had me acknowledge that my wellness exam would cost $350 or something in the event insurance did not pay for it, and there were posters up informing people that they have a right to ask for a good faith estimate.