if you already have a Thai bank account, then transfer 800,000 THB onto it from abroad, make sure it is coded as a foreign remittance. As soon as the money is in the account, make a border run, enter visa-exempt, then you can apply for the "change of visa type" from the exempt entry to a 90-days Non-Imm-O visa on Immigration for 2000 THB. You won't need an agent. It is however better to use an agent as they can make the process seamless and easy for you
"you can enter on a 60 days visa exemption and apply for a Non O inside Thailand. You’ll probably need a visa agency to assist you as you’ll not be able to open a bank account without a long stay visa." . . . . . it is NOT POSSIBLE anymore, even with the help of any agent. All agencies discontinued offering "change of visa type" from a touristic entry to a 90-days Non-Imm-O visa. You need a Thai bank account for it, and even agents now cannot circumvene this process. Thai Visa Centre in Bangkok was the last one and they have stopped offering it
I copied the Bangkok Post article from January this year when they warned foreigners of impeding accounts closings and impeding disabling of online banking. It's been in the Thai media from December thru March. A deadline was announced and this was April 30th you were given time to clear everything inside your local bank branch
no, you probably misunderstood the agent. If you use your own funds of 800,000 THB in your Thai bank account, the agent helps you with bank account opening and the application to the 1-year Extension of Stay for 16,500 THB. If the agent has to front the money, you would pay at least something like 32,000 THB. Opening the bank account only would cost something like 5000 to 7000 THB. The fee on Immigration for the application to the Extension, is 1900.-THB. In case you use own funds, then you actually would not even need an agent. You would just use the agent for a seamless account opening, and apply for the 1-year Extension by yourself 60 days after the money was paid into the account