My being married to a Thai, on a 'permission to stay' extension on a Type-OA visa, what I did, to avoid that 3,000,000 insurance requirement was to go for an extension based on marriage to a Thai. I was able to do this (last extension based on marriage instead of based on retirement) without leaving Thailand.
I have great subsidized Health Insurance from a European Health Insurance company (superior to the 3,000,000 THB coverage), where there is a Thai branch of the Insurance company on the Thai list, but the European branch refuses to issue appropriate paperwork for Thailand (and refuse to fill in the Thai database).
The Thailand branch (same Health Insurance mother company) refuses to issue me appropriate paperwork for Thailand (and refuses to fill in Thai database for me) for their mother company in Europe. There is no money in it for their branch of the company, so they refuse. When I asked how much they wanted to do the paperwork/fill in database, it was a full (double) 3,000,000 insurance from them.
Obviously I wasn't interested in double Health Insurance AND I did not want to stop my superior subsidized European Health insurance (with the same company but a branch located in Europe) , so I elected to go for the 'extension of my permission to stay' based on marriage.
I also want to add - I have visited a couple different Thai hospitals in Thailand, and without exception the Thai hospitals have accepted my European Health Insurance.
I have some international travel coming up, and I am debating if I will let my Type-OA expire (when I exit Thailand) and then try to go for a Type-O shortly after a re-entery Visa Exempt. However timing of my various travel complicates this ... so I am puzzling over it.
If international travel is an option for you, then you could consider leaving Thailand to invalidate your Type-OA and then re-enter Tourist Visa exempt, and immediately attempt the Type-O visa route, to avoid this health insurance requirement. I think if you already have good health insurance (like myself) or have massive financial savings in the bank (for a self insurance) than such an effort to change to a Type-O visa (based on retirement) is an acceptable "moral" approach.
I wish the Thailand implementation of the Health Insurance proof would better accept European coverage (for when in Thailand) and also accept Self Insurance (by maintaining large amount of money in a Thai bank).