My brother and went there a few years ago. The biggest expense was the flight there and back. Within Thialand, we were able to get around cheap. Flights from Chiang Mia to the islands, or anywhere out of Bangkok, were around $50-$70. Food and lodging were way less than half what you'd pay here. A lot of expats there.
Though, yeah, as soon as I stepped off the plane, I went back to a pack a day habit for about ten days. But, a pack of smokes were only around $2.