One other thought.
I'm on "traditional" medicare here - part A (hospital) that has no premium cost for me and is based on my work history; part B (doctors/labs, etc.) that I pay $165 a month for whether I use any of it or not but that only covers 80% of the Medicare-billed costs (which are much lower than the walk-in-off-the-street-without-Medicare charges); part D (drug coverage) that I pay about $10 a month for (but that has no cost for my routine medicines and $5 for the occasional other med). I also pay $210 a month for a "Medigap" plan that covers all expenses that medicare would leave me - the 20% co-pay for part B services, lengthy hospital care, etc. So I'm paying basically just under $400 per month for my health coverage. It could be much cheaper if I did a medicare "Advantage" plan, but those are too much like HMOs for my tastes, and come with all sorts of "gotchas" that you have to pay attention to before selecting a plan. If I was living in California, I'd just switch over to Kaiser, which would be at no cost at all to me other than a $5 per visit co-pay as my old employer would pick up the costs. (The downside is that Kaiser is a HMO.)
All that said, there are other HMOs that might be of use to you. Kaiser is one that comes to mind. They are not everywhere, but there may be an organization that is in the place you want to call home here. I remember looking at Kaiser last year for a friend and her husband, and it was going to cost them about $700 a month for cover (for the both of them) and only very low co-pays per visit. I believe expenses were capped at about $7,000 per year (they had no deductible, so this was if the co-pays or charges for medicine hit $7K, with a reminder that preventative care is free). If they managed to run up bills to that amount anything above it would be at no cost.
Because they were relatively low income (about $50,000 total per year) they qualified for government subsidies to cover almost the complete cost of the monthly premium.
TLDR answer is, don't assume Medicare is your only option. If you have a general idea where you might want to settle in the USA, check for alternative options there. Good luck!