Vietnam is the cheapest country to live in Asia. Da Nang is the most affordable "world-class" beach in the world. WFH should be about beaches or mountains or museums depending on your taste.
- Central America is a convenient plane hop away, and in the same timezone.
- Parts of Africa and India are anglophone, which makes life easy. Africa is at least somewhat timezone compatible (calls might cut into evening plans, but you don't lose sleep)
The cost-of-living relative to Vietnam is low enough to not matter. There are also middle-income countries where cost-of-living is a bit higher, but with much better infrastructure. Plenty of Southern and Eastern Europe is at about a third of the per-capita GDP of the US.
There are few advantages to living in SF.