As for CoL costs it totally varies. Some of the local people I hire can live off their salary of $700 a month. A comfortable western lifestyle would be about $3k a month, imo. I spend a lot more due to travel.
He's running his businesses in a tax efficient way so he's keeping a lot more of his money than when living in CA.
Now I haven't been to Thailand, but in Vietnam you could live very, very comfortably for half that.
Some western foods for example are highly priced compared to local options: imported au/us beef is similar cost to Australia ($20-$30 a serve) but local "steak" is maybe $3 to $4 a serve. It also has the consistency of a finely barbecued shoe.
It also depends on the area. A lot of expats want to live in areas surrounded by other expats, so things are priced higher in general.
If you go live "in the sticks" ie you will stand out as one of few/only foreigners in the district, things can be cheaper (once people know you're a "local")