In Thailand it depends on where you live as well. I absolutely love ChiangMai - would choose that town over BKK in a heartbeat. And it was dramatically cheaper but obviously quieter, not as lively.
As for cheap in Asia ... Indonesia, particularly on the main island of Java is dirt, dirt, dirt, cheap if you can go local. Then again, you sacrifice clean air, convenient access to some western goods, a degree of personal safety, and you have to function in perhaps the most corrupt country on earth. A few years back we stayed at a ... Hyatt or Shangri-la (?) in Jokyakarta (sp?) for like US$25 a night, with breakfast included. That was a local rate. You can hire a contract wife (or two, no joke ...) and then avail yourself of those kind of rates. I've been told your contract wife will also procreate for you should that be your thing ... My relatives in Jakarta have live-in and live-out maids for ~US$20 per month. Full-time drivers and nannies as well. Thus Indo seems awefully cheap if you just look at price, but ignore value.
Malaysia can be cheap but ... why?
Cambodia is certainly cheap ....
I'm in Singapore now and find the cost / quality of life to be extremely good as far as Asia goes. Also, it is a short hop to anywere else I want to be. Singapore can be as cheap or as expensive as you need it to be - which is just right for me. And it is clean, safe, and extremely expat friendly. If you have a family Singapore is probably your best bet.
Would think that the PI could also be cheap, that is if you localize ...
Vietnam should also be cheap ... damn I need to make it out there soon.