I don't know where you're getting the idea that this legislation would involve the government in purchasing medical care. It relaxes the standards for people to qualify for Medicaid somewhat, and sets up exchanges that people can use to pool risk and negotiate with private insurers to cover all of them, but doesn't actually set up new programs for federal purchasing of medical care and services.
The exchanges will be overseen by the government, and government is "purchasing" in a way as they are subsidizing premiums. IMO, to achieve cost control there will have to be rationing, either through this bill or in future bill. As far as spending, we're so far underwater already this is like adding a tea cup to a pool.
From the link I posted earlier.