Provided that financials are in order, it would be 1900 baht for the yearly extension, 1000 baht more IIRC for a single re-entry permit ( if needed ). It's just a matter of getting all the paperwork correct. Your choice, I don't throw away money.
The normal price is on all the official Thai Government immigration information, and it is 1900 baht a year. The checkins are no big deal and you can leave those off for a 2000 baht fine. The money in the bank is less than a million baht.
Where is your 3800 coming from? I don't pay anything but 1900 yearly...if I leave, 1000 more. Works fine for me, and everyone I know...if you want to spend more..go ahead.
To each his own. I pay 66,00 per year, where is the 5700 coming from? What perks, saving money is a big perk. 10 years at 66.00 per year is only 660. USD. I pay less than 700 for TEN years, and, it is the normal way to do it, easy, and without agents....never had any problems.