Look outside the US, and you will find that your solution (primary care done by nurses) isn't unlikely to be the right one.

In France, going to the doctor (general practitioner) costs €22, before insurance (it's €5 or €1 after insurance, the co-pay as you'd call it). It's much cheaper because:

- he didn't have to spend 200k to go to med school, it's free

- he doesn't need 5 employees to fill insurance forms, or waste 2h a day calling insurers -- it's all automagic, no paper involved.