Back in the 50s MDs had nice houses and cars but one could more easily pay out of pocket med bills. Nowadays over and above malpractice insurance, the accounting costs/staff add plenty to private practice costs.
In the end the market sets the price and the best MDs can charge plenty because they have more patients desiring them than they can possibly serve. High prices help weed out the field.
IMO, it still does not change the fact that the doctors could give lower rates for people who can or have to pay out-of-pocket. There is less administrative cost for accepting cash. They make enough money off of insurance companies to still live comfortably.
They still live in nice houses and drive nice cars. I have yet to see a doctor driving an old junker or living in a low-income area.
I for one wouldn't mind paying $50 or so for an office visit as long as it helps to keep the cost of medical insurance down.