I live half the year in Vietnam, half the year in NYC. I'm mildly frugal, but Vietnam still runs me about $2K a month, $1.2k if I don't leave my apartment. NYC, a frugal month costs me $3.5k.
SE Asia is cheap, but its not as cheap as people think it is.
My wife and I spent a month in Thailand a few years back. We paid $120 for an apartment in Bangkok for the month, including utilities, and spent about $6/day on food. Travel to and hotels in Laos, N. Thailand, a beach town, and Cambodia probably cost us about $300.
I do speak the language, but that only helped with finding a cheap (i.e. Thai-priced) place to rent.
There you go. Things develop at light speed down here in SE Asia!
That being said, GP's version of Vietnam living is perhaps like my Phnom Penh version: "costing as I would in Europe, but get way more bang for the buck" (to qualify---not that kind of bang, thank you very much..)
So down here I can get a furnished condo thingy with pool/gym/view/flatscreen/balcony for the same bucks that would get me an unfurnished hole without all of these in say Berlin, to not even mention other parts of Europe.
BUT, it's still a multiple of $120. If I were harder-pressed financially, indeed $120 would also rent me .. "something".
I knew a guy that would spend half the year living in Bali. He's a trippy-hippy dude who makes his money doing astrology readings.
Even though it didn't really fit in to how he wanted to live his life, he ended up getting a local housekeeper. She'd basically just do all of his shopping (groceries, clothing, whatever) and pay the local price, rather than the tourist price. With the money he saved, he paid her above market rates and still managed to save money on the whole deal.
SE Asia is cheap, but its not as cheap as people think it is.