This is the question you believe any reform proposal should answer? How we can we find ways to keep spending the exact same amount of money, year after year?
What I'm saying is single payer is unlikely to address the issue prices charged by providers. There is no economic mechanism in single payer that would drive what hospitals charge down (though I suppose one could argue there is a lega, authoritarian one if government was so inclined). So if the providers are going to charge the same but the intent is to keep employers from having to pay insurance premiums for employees and for citizens costs to go down, the difference has to be made up somehow. The only way I can see to do that is either raise taxes on people or continue to borrow and add to the debt.
I'm not familiar with any single-payer proposals that involve providers retaining the tremendous power they currently have over prices. In fact, that's generally one of the primary arguments offered in favor of single payer proposals. At present, prices (i.e. reimbursement rates) are dictated by provider market power relative to payers; different payers will often be charged different reimbursement rates for a single service based on how much of the insurance market they have cornered. That isn't the case, at least with hospitals, in the only state that currently has all-payer rate-setting (i.e. common reimbursements for all payers set by the state); and in that state, they're not bent quite as far over the barrel by hospitals:
On average, Maryland hospitals charged patients 20% above the cost to treat them in 2007, compared with a national average of 182%, according to the American Hospital Association.
If you're going to have a bilateral oligopoly, there are advantages to at least have a public entity refereeing; single-payer takes the concept further to pursue some other benefits beyond simply shifting the power to set prices away from providers.
Again other than artifical authoritarian power, what market force is going to drive provider prices down simple by makng government the single payer? It would seem to me that would give providers even more leverage because they know they are deaing with a payer that has one gigantic pool of taxpayer money and doesn't seem to care too much about going into debt to pay for things.