This study
($30 for full text) looked at Emergency Department (ED) visit costs,
and whether increased visit volumes exhibit economies of scale, i.e.,
result in lower costs per visit. The issue driving this inquiry is the
number of outpatient ED visits and whether it is more cost effective to
treat those patients in the emergency room or in an ambulatory clinic
setting.
The investigators found that ED visits cost $295 and $412 for non
trauma and trauma EDs respectively (that's in 1998 dollars). These
costs are more than double the cost of treatment in an ambulatory care
setting.

Our findings suggest that the marginal cost of an outpatient ED visit
is higher than is generally believed. Hospitals thus need to carefully
review how EDs fit within their overall operations and cost structure
and may need to pay special attention to policies and procedures that
guide the delivery of non urgent care through the ED.