Cost of life in Vietnam is extremely low for western standards. This may change in the future, because the country is developing fast. Although prices are low, the fact that locals tend to pay less, upsets some tourists.
Some visitors I met told me they always had the impression they were being cheated. During my stay in Vietnam, I could see how in some cases foreigners were charged more (taxis, museums, and hotels), but in many other cases they were charged the same (local cafes, restaurants). The question is that for some backpackers a good deal, means getting something for almost nothing. They want to get the "local" price, but sometimes and in some places local prices are not that cheap.