I think if you move to Vietnam from China, then you can expect similar low-cost living.
Just to give you an idea of
the cost of living in Vietnam:
- 30m2 apartment in Ho Chi Minh City - 7 million dongs (USD450).
- Packet of cigarettes / Beer / A meal out - less than USD1 each.
- Internet is cheap and everywhere in Vietnam. An internet cafe would be about 3000 dong per hour. For ADSL connection at home, the price is from $30~$65 / month depending on the speeds you need.
Avoid drinking tap-water as water borne diseases are quite common in Vietnam.
When renting, just make sure the landlord or real-estate agent has the legal right to rent to you.
Availability of Work
Like most countries, this would be concentrated around the cities and urban areas. Largest city is Ho Chi Minh City, or previously known as Saigon with just under 3.5 million people. Next in line would be Hanoi with 1.4 million people.
Ho Chi Minh City and Hanoi have a lot a language schools looking for native English teachers that hold a university degree. Depending on how picky you are, you can easily get a full-time or part-time contract.
Other
Hanoi (monsoonal climate) would be your cheapest access point as it's in northern Vietnam, just a stone's throw away from China. Ho Chi Minh City (tropical climate) on the other hand is way down south.
Vietnam is quite a poor country with somewhat 15% below the poverty line. The average yearly salary is about USD3,500, so don't expect to earn too much as an English teacher.
So what do you think? Similar to China?