Is it really possible to survive on $20?

Yes, but you have no buffer for emergencies or private transport. If you want comfort, increase the budget to $35.

How do I move between cities cheaply?

Use the overnight sleeper buses. They are cheap, reliable, and save you the cost of a hotel room for the night.

Vietnam on $20 a Day: The Practical Strategy

To survive on $20 a day in Vietnam, you must stay in hostel dorms, travel exclusively by overnight bus or train, and eat exclusively from street stalls. It requires discipline, but it is entirely possible if you avoid tourist-heavy cafes and alcohol.

Secure budget accommodation. Book hostel dorm beds in advance via apps like Hostelworld or Agoda, aiming for the $5–$7 range. Look for places that include breakfast to save another $2 on your daily food budget.
Eat like a local. Avoid 'tourist' restaurants. Stick to plastic stools on the sidewalk. A bowl of pho or a Banh Mi should cost between $1 and $2. Drink local 'Bia Hoi' (fresh beer) or, better yet, water from your own reusable bottle.
Master ground transport. Use the 'Sleeping Bus' network for long distances. It doubles as your accommodation for the night, saving you the cost of a bed. Book via local travel agencies or sites like 12Go.Asia.
Limit alcohol and tours. Alcohol is the budget killer. One cocktail can equal two full meals. Skip organized tours and explore cities on foot or by renting a bicycle for $2 per day instead of taking Grab taxis.

Is it really possible to survive on $20?: Yes, but you have no buffer for emergencies or private transport. If you want comfort, increase the budget to $35.
How do I move between cities cheaply?: Use the overnight sleeper buses. They are cheap, reliable, and save you the cost of a hotel room for the night.