The ER in any hospital is hugely expensive to operate and inner-city ERs are even more expensive to operate. Many hospitals, including where I volunteer, have out-sourced their ER, directly paying only the salary of their employees.
A trend of concern for hospitals is their ERs have become a doctor's visit for those who do not have/cannot afford health insurance. How this growing overload in ERs effects patients is clearly visable - wait times have increased...If you arrive via ambulance, the ER has received a heads-up you're on the way and chances are good you will get pushed to the top of the list.