Not exactly. The ER is required to provide a screening medical exam, and stabilization of any emergent medical condition. So if you show up with a non emergent condition they gave every right to do the screening then show you the door.
If its not an emergency, then I am not sure why you are at the ER or why you need to worry about immediate treatment. More and more doctors are willing to take cash at a discount as are urgent care facilities. Frankly in many socialized countries there is a whole tier or private clinics that provide the real high quality care. No one in their right mind would go to the hospital in some of those locations.