Do you have the required 800,000 in the bank and willing to leave it there all the time?
if so no need for an agent, an just pay 1,900/year for the extension AND
pay 1,000 baht for single re entry or 3,800 for multiple
IF no 800,000, than its a min of 16,000 baht/year, PLUS the re entry>
you do the math