Robert Lagas, for the previous 10 years on Non-O AGE extensions Mae Sot, and now Sukhothai, immigration have required 800k baht in my account for 3 MONTHS prior to extension.
I have questioned this on occasions with the same answer. Even as recently as May this year I was given a print-out of the new rules and that STATED 3 months prior.
Yes, Don Muang has an office for re-entry permits (same office as for over-stays) after you pass through immigration towards the left-hand end of the wall. Office hours I couldn't guarantee but as it is over-stay as well I would suggest it is open as long as passport control is operating.