If you can save $10 by paying $5, and your argument for why you won't do it is that it costs too much, I'm going to tell you that you need a math course.
What it seems to actually boil down to is bribery.
It's not simple math though, it's politics and projections from people with an agenda. If you tell me I can save $10 by paying $5, it's my responsibility to decide if you're lying to me, to question your assumptions, etc. Maybe it costs $8 to save $10, but I give up significant other rights/options/etc.
TLDR, it's not just math, and the math isn't that simple.
But you won't be saving money. Think of it as a conservation of matter problem in physics.
The current insurance model covers some set of care for some subset of people. The goal is to provide more comprehensive care for more people - i.e., much more care will be provided in total. The supporters of government-provided healthcare (whether it's this CA bill, or ACA) don't want to look at this bigger picture and acknowledge that they really are proposing to spend a lot more.
Not only will this cost more, but pushing more care through the existing infrastructure will also result in long waits for care and the other kinds of things people in Canada and the UK complain about. If the infrastructure was built with a given amount of usage, vastly increasing that usage will overtax the infrastructure. And with the financial concerns that surround the problem, it's quite a stretch to say that the capacity will be increased.
Your implication is that because they're the only buyer, sellers will be forced to fall into line. That's not applicable in this situation, for the very same reasons that the bill's proponents claim that a free market system doesn't work.
For the negotiation that you're implying to work, it has to involve the possibility that the potential buyer could say "no" and walk away. In this case, it's not going to happen. There's just no way the government can say no to, e.g., a revolutionary treatment for AIDS - the political constituencies simply won't let it happen.
So what we'll be left with is:
- Treatments for maladies involving well-organized constituencies will get disproportionately better coverage. So AIDS or breast cancer will have much better care than, say, colon cancer.
- The choices in these negotiations will be made by those hyperbolic "death panels". Yes, the GOP were exaggerating a lot, but when it comes down to it, somebody has to decide where finite resources will be spent. Somebody in the government is going to be deciding if your affliction is the one that gets left on the negotiating table in order to close the deal.
I wish I had $1 for every time someone told me I was "guaranteed" to save $10 later by paying $5 today.
Now, instead of an alleged guarantee, let's change that to "we admit we don't even have a concrete budget estimate that demonstrates how this will save money, but take our word for it that at some point it'll pay off. And in the mean time, we need to triple the state annual budget". That's a much harder sell, especially at this scale, and especially when the majority of people are actually satisfied with their personal insurance situation as it is.