If you have already an insurance in the US and that insurance is still valid, you can have a a good local medical insurance in Thailand with largely reduced price.
Taking a local health insurance with deduction. This would be the effective both for cost and coverage. You will pay less while having a good coverage.
Contact me if you want a basic coverage for your worst case scenario. I’m an agent with Allianz Thailand and able to propose some things, at least to compare.