This is an important problem with trying to price healthcare according to “marginal cost.” What is the marginal cost of professional labor? Physician time is not an IV bag with a wholesale acquisition cost. Its economic cost is the value of the next best use of that time. I know what the market will pay me for consulting. I know what hospitals will pay for call coverage. I know what alternative clinical work pays. Those do not mechanically determine the correct price for neurosurgery, but they provide information about the opportunity cost of my time. In the short run, the “marginal cost” of asking an already employed surgeon to do another case might appear very low. Price every case that way and eventually there will be no surgeon standing there. For No Surprises Act IDR, the better question is “What would a physician and insurer have voluntarily negotiated before the emergency, in a competitive market where neither could exploit the patient?” There is no easy answer.