That's a very vague question. Can you describe your circumstances a bit more? Are you visiting the US? Moving to the US? Working in the US? These circumstances would have different answers.
For most FIREd, the answer would be a plan through the Affordable Care Act. These are generally "affordable" through government subsidies. But those subsidies have requirements. And if you don't have income reportable for US tax purposes, the system may think you are destitute and route you toward Medicaid, the medical program for low-income people--which will have its own qualifications.
From:
https://www.ehealthinsurance.com/resources/affordable-care-act/aca-obamacare-subsidies#:~:text=To%20qualify%20for%20Obamacare%20premium,%2C%20Medicare%2C%20or%20Medicaid).
Who qualifies for ACA (Obamacare) subsidies?
To qualify for Obamacare premium tax credit, you must be an American citizen or legally present non-citizen living in the United States who does not have access to other affordable health insurance (for example, an employer-sponsored group health plan, Medicare, or Medicaid). In 2023, a job-based health plan is considered “affordable” if your share of the monthly premium in the lowest-cost plan offered by the employer is less than 9.12% of your household income. The lowest-cost plan must also meet the minimum value standard.
You do not qualify for premium tax credit if any of the following circumstances is true:
You are married and filing taxes separately (except in cases of spousal abuse or abandonment) or refuse to file income tax;
You are incarcerated;
You have access to affordable employer-sponsored insurance but want to purchase family insurance because you can’t afford the cost-share for family coverage under the employer group health plan.
