I have lived in Thailand for 15 years, have used the Combo method every time , first in BKK for 5 years then 10 years in Pattaya, Jomtien Immigration I am Australian so can not get an letter from the Australian Embassy, I have money in the Thai bank and money deposited each 28 days into my Thai bank that make up to over 800,000 Baht for the year, Centerlink in Australia arranged to deposit my pension direct into my Thai bank , Kasikornbank, I get a statement from the Kasikornbank, for the full 12 months that show all deposits, and the money in the bank , must have two letters from the bank , one for the deposits and one for the money in the bank, never had a problem, never used an agent ever always do it myself, so easy, ,, this is only my experience at Jomtien Chon Buri only may not work at all Immigration places. if any one wants to contact me they can I maybe able to help. OP may not be able to use this method as he may not have the income and money in the bank long enough,