What about the visa? My experience is that cheap countries get incredibly expensive if you need broadband and a reasonably secure neighbourhood. Or are you talking about living in a hotel on a tourist visa? That only works for 3 to 6 months and I'm not sure it's possible continue working for a NY startup whilst in Thailand.
We stayed in Chaing Mai for about a month, had broadband access. The people we were staying with were renting a large house for about $400 a month. You can take a weekend trip to Cambodia or Vietnam and get a renewed visa when you come back. Or travel around SE Asia in general. You can do that indefinitely and it's quite cheap, even in relatively urban areas. Definitely cheaper than NYC(!)
Why not try India instead? The national language is English so it should be of little problem, plus everything there is super cheap. Buy a bicycle for $10 brand new and there's your transportation.
