Daniel Armstrong. Which is why I said "legally". There are plenty of news articles already about foreigners who have been caught illegally drinking in bars and restaurants, and they start crying when they're arrested and fined. I don't know if any people on Samui are going to list the bars that are illegally selling alcohol!
Benjamin Hays. It's two months before the date of application, not necessarily the expiry date of the entry stamp. So if the OP goes early to apply, he must ensure the 800k has already been in the bank for two months
Dave Haynes. If it's first extension from the original visa, it's two months before date of application that the 800k needs to be in the bank, and three months after.
. The biggest problem is once you start using an agent, you're stuck with them until such time as you can leave the country and come back in on a legitimate visa. It's a bottomless pit you have to keep throwing money into.