do you have your own 800,000 THB funds? If not, you can expect a price of 28,000 to 32,000 THB for an agent service which you use for the first time. Follow up annual extension will then be cheaper, like 14,000 to 18,000 THB
okay. . . then choose any time during the year that suits your needs. Just observe the timeline: 90 days from entry, and the extension will start exactly one day after the 90-dys stay pwrmit expires. A date which will remain in the future
for the LAST TIME: You don't have any visa in your passport. Your visa is a .pdf document issued by a Thai embassy. There is no visa in your passport. Understand now?
in the old days, the visa was a sticker in your passport. Immigration was NEVER allowed to transfer this sticker, they didn't even have any supply of these stickers! The sticker were issued by the Thai Embassies abroad. You entered with both passports and received you entry stamp into the new passport. In case you were already on a "1-year extension of stay", this was (and still is!) a stamp from Immigration, and this is the only thing Immigration is allowed to duplicate (transfer) into your new passort
you are totally wrong. There is no "Thai visa" in your passport. There is only an entry stamp from Immigration that says "admitted until" with the expirty of the stay permit in blue ink. In case you are already on a "1-year extension of stay", then you have no visa, you have an "extended stay permit" in your passport, which is a stamp Immigration is allowed to transfer from the old to the new passport. The visa you used when you entered is already invalid and thus can neither get transferred nor extended.