Can someone provide a reputable source for the average cost (not
co-pay) of a visit to a primary care physician in the US?  There is a
$60 widely cited and initially published by the AMA that is not high
enough.

That figure might be in the ballpark if you go with what insurance
companies allow, not what the actual billed charge is, and exclude any
labs or other services performed. For example, Medicare allows $51.75
for a typical office visit for a moderate problem. Providers can of
course bill whatever they feel like, but unless the patient doesn't
have insurance or the provider doesn't participate with the insurance
the provider eats the excess charges, so for most patients they don't
have any basis in reality.