If it's not too expensive, then there must be another reason that it hasn't been implemented in blue states.
Subsidized/free universal coverage only really works if everyone gets it and everyone pays for it. If my state pays for it but anyone can come here and take advantage, then my state system will collapse.
They need some way to exclude out out state people from getting free healthcare. Countries with universal coverage accomplish this with immigration restrictions and citizenship requirements, but the US is built on free markets operating across state lines. If you live in NJ but could get free care from NY or PA taxpayers, you are likely to abuse the system.
The "universal" part of universal health care means paid for by everyone, not just available to everyone.
Why would anyone be allowed to use it? Why would it not be open only to residents of that state? No different if someone is a visitor to Canada; they don't get free healthcare just because they drove up to Toronto for the weekend. Again, blue states are already paying for far more than their citizens use, so a little bit of abuse, which is probably inevitable in any system, wouldn't destroy the program. As was pointed out, Canada did this very thing at a province by province level - didn't collapse their system.
I'm not even saying full single-payer system either; what about a state that just completely subsidized insurance for everyone? I mean, one example of universal health insurance/coverage being adopted by a state other than a Republican state. I have not heard of one.
I just don't buy the argument that 'We, the richest states in the Union (who pay to fund the entire government) can't afford it without those broke red states we already give money to pitching in money they don't have. Also, we want them to have it too, so if everybody can't have it, then no one can.' I mean, the Federal Government gets all of its money from citizens and the states, so it would be the same money just circulating a different direction.