I see. Yes, you'll definitely need 400,000 baht in the bank and it will need seasoning too. I had to show that the money I transferred to the Kasikorn bank had come from overseas and in order to get the Non O visa based on marriage to a Thai national, it had to sit there for 2 months before my application . I didn't use an agent but some do and I believe they " lend " you the money but then I believe you are then stuck with them for each renewal.