I stayed in Thailand from 1998 to 2009, periodically without having to show any money in my Thai account, or 800k, but then I wasn't staying there as a tourist who wasn't savvy about how to stay long term. Those were the good old days.
I posted on this issue yesterday regarding if you are a pensioner in the UK and pay some tax, then you won't pay any tax in Thailand. So I commented, so if your in receipt of only a UK state pension that isn't taxed in the UK, surely you wouldn't be liable to pay any tax on it in Thailand. The lady said that even if your not liable for tax in the UK because your income is below the UK threshold, you'd still be liable for tax on anything over 150k baht.?
Whichever way you get a visa extension you are still contributing to the Thai economy. As long as your self sufficient and can prove you have a regular income of some sort, that's what matters. Years ago, the amount of money you had to have in a Thai account was only 200k, or 20k a month income. Then they decided I presume to increase it by four times and I reckon they based there new rules based on Americans who have a lot more disposable income than most pensioners from other countries.