Depending on how you wanna stay. Hotel from usd3 to few hundreds, you can find many cheap hotels, hostels, package tours in old quarter (many streets begin with "Hang") in Hanoi or in Bui Vien str, De Tham str in Ho Chi Minh city.

Meals from less than usd1 to usd10 per pax - normal range for both Vietnamese (city ppl) and foreigners. If you need some thing special, high class, preparing yourself for same price in developed world.