That's just gross. That's a back-of-an-envelope thing that a few health economists and physicians and folks who have been talking about public medicare have come up with that they think could cover 150 essential medications. It doesn't include whatever you may be able to extract by thinking about the tax subsidies that go to private health insurers and it doesn't include the other benefits.
On your last question, I would note with respect to integration and controlling or attempting to moderate physicians' prescribing budgets that private health insurers don't have the ability to do that at present.