True, although that money (400,000) has to have been in the bank for two months prior to the date of extension. i.e. you have one month after entry to Thailand to get the money into a Thai bank.
You really need to supply a few more details if you expect a sensible answer here. :) How old are you? How long is "as long as possible"? i.e. are you looking at an extended holiday or to settle here for life? How much are you willing/able to spend? etc.
While it might not seem to make sense, the fact is that Thailand has one of the lowest death rates in the world from the virus, so whatever they are doing is at least effective.