It really depends where you choose to live. Phuket and Samui will cost you more for restaurant food and drinks. Bangkok will cost you more than Chiang Mai and Chiang Rai. And everywhere will be more expensive than Isan. It depends how you want to live? Drink wine? Eat cheese. Or eat like a local without eating Western food regularly. Are you going to buy a car or motorbike? Will you be paying for adequate health insurance? A major accident or illness could heavily dent your savings. It really is a difficult question for anyone to answer if they don't know your tastes and lifestyle preferences.
it's very frustrating, but rather than blame our embassies we should blame our own citizens who previously lied when declaring their income / funds. Which prompted Thai immigration to insist on embassy verified income, paperwork
however if he has already transferred all of his money to his wife in Thailand, he may no longer meet the financial requirements for obtaining an OA visa in the US ie if he no longer has the equivalent of the 800K baht in the US, so it might be a moot point
actually that's probably what I have been doing wrong ie not using an agent to pay the bank teller to facilitate getting my yearly statement. The last two years my statement has taken between 11 and 18 days to arrive from Bangkok Bank. Both years I have had a frustrating series of repeat visits to the bank where it appears that they had lost my statement or hadn't sent a request for my statement to the head office in Bangkok
I imagine that the one posting is usimg an agent to assist them getting a retirement or marriage visa. The bank statement is a part of this. Has to be in a particular format, ordered from your bank about a week before you go to immigration. Has to include every transaction you have made in the previous 12 months. Have never heard of anyone being able to use bank statements they have downloaded from internet banking as proof of funds for long term visas and 12 month extensions, however I guess it is possible that some immigration offices are less finniky than others