I'm the husband of ML, and have worked in health insurance for years.
Insurance is heavily regulated at the state level, so health insurance companies offer vastly different policies in each state. Any answers anyone gives you about rates or availability or coverage would differ drastically from state to state.
Because almost everyone in the US qualifies for Medicare at age 65, insurance companies don't bother spending their time selling 65+ policies. It's almost impossible to find non-medicare insurance for petitioned parents from well known insurance companies, unless you happen to live in a state that requires such policies to exist.
After 5 years, petitioned GC parents can qualify for medicare at the non-subsidized price (I think it's around $700 more per month than most people pay). Your parents would have needed 10 years of work in the US (paying the medicare tax) to qualify for the subsidized rate. Once qualified for medicare (even if non-subsidized), there is usually a large array of insurance options available from the government and private companies, and medicare.gov has a tool that lists all of them for a given zip code.
What many people do is just leave their parents uninsured. Emergency Medicaid pays for emergency room visits and subsequent hospitalizations for anyone without their own income (income of kids is ignored), and it is exempt from the affidavit of support contract.
States offer regular medicaid that pays for no-income individuals, but many states prohibit green card holders from signing up in the first 5 years, and technically the states could sue the GC sponsors for reimbursement for medical treatment (although no one I spoke to has heard of it happening). States routinely sue the patients (and their estates if they die) for Medicaid reimbursement from any of their assets.
For people who lost their job, individual insurance is exorbitantly expensive, because it is usually only purchased by sick people. For kids, some private insurers have reasonable rates, but its usually hard to beat COBRA. COBRA, which allows you to continue your prior employer's insurance for 18 months, is usually much cheaper than individual insurance, because all the healthy people in your prior employer still subsidize the rate.
-husband of ML
