If I went to an emergency room in the United States, roughly what fee
would I have to pay to the emergency room physician for his/her
assessment and treatment of me, assuming I had a straightforward
problem that didn't require testing or procedures (e.g. the flu)?

This assumes I am uninsured and paying cash.  This is not the total
fee, just the portion that the emergency physician would receive, or
at least the portion that would be billed in his/her name (assuming
he/she was not on salary or other alternative arrangement).

This would not be the same as the physician fee that medicare would
pay in this situation, although that would also be useful to know.

I understand that these fees may vary widely, so a couple (e.g. 2-3)
examples from different places would be good.

A Washington DC suburb (Greenbelt, about 6 miles NNE of Washington DC)
emergency vist recently had a "medical screening" charge of $50 and an
"E/R visit-- beyond screening" charge of $238. There was another
charge called "ER beyond EMTALA" for $238 and a deleted charge ALSO
called "E/R visit-- beyond screening" for $182.

An examination of the insurance benefit shows only one charge of $238
allowed and describes it as "Emergency room", but does not specify
which charge it is. The amount covered was $234.67 and $49.30 for the
medical screening.

I suspect these fees wouldn't be going just toward the emergency
physician, but rather to the hospital in general (infrastructure,
salaries etc.), of which the doctor would get some fraction.