@Steve ****************
unfortunately, you either misunderstood or were told incorrectly. :/
IF you have the 400K baht in a thai bank account for 2 months before you apply you can get a yearly extension of stay.
You would apply when you have 30 days or less left on your current stamp. It would go under consideration for 30 days and then you would go back and get the year extension stamped into your passport. It costs 1900baht.
You would however have to start doing 90 day reporting (IF you were in the country for 90 days or more). :O
AND if you're going to exit/re-enter the country during the year's extension you would need to get a re-entry permit (either a single entry for 1000 baht or a multiple entry for 3800 baht).
Exiting the country after you get the year extension without a re-entry permit would cancel your extension.