Easy to get annual emergency cover for that kind of money if you are say, a UK citizen, have a UK address, are registered with a UK doctor and are mid 60's or under.
The problem comes when you get to about 66 or so. Then they don't want to know you on long term stays at anything like that low price.
As a guess, if anyone really had to self insure, I would throw the figure of 4 or 5 million Baht in the ring as the minimum that should get you out of 99% of problems. I have personally known farangs over the years who have spent over 5 million Baht on one hospital stay, rare though that is.. Long term in ICU / intensive care after stroke or road accident etc etc. Then they may have the problem of needing an air ambulance home. Mega money. (Would be interested to hear what Sheryl has to say on that)
I would never go to Thailand without some kind of insurance anyway. Many companies will give lower prices the higher the excess you will pay.
Health insurance concerns are one of the reasons I am now, after a very long time in Thailand, splitting my time between there and UK.
I could self insure at the sum I mentioned easily enough but much as I love Thailand it's just not as much as I used to, what with all the air pollution and changes there over the years, and certainly not 4 million Bahts worth.
Going for 3 months at a time still only costs me something like £300 in travel insurance for millions of GBP of medical cover.
For some strange reason, after more than 30 years of hating going back to the UK and gagging to get back to Thailand anytime I had to, it just doesn't seem so bad anymore. A shadow of it's former self though it is it will take care of me if I fall down now I am getting older rather than telling me to drop dead unless I can pay enough, as in Thailand.
Yes, the weather can leave a lot to be desired but compared to the deadly air pollution in Thailand these days it's actually preferable a lot of the time.
Not that cold weather worries me when I make sure the UK house is at least 25 degrees day and night anyway.