Quick answer: Da Nang runs about EUR 45 per day mid-range - noticeably less if you eat local and walk. Cheapest window: February-May - dry and warm before the peak summer heat; September-December brings rain and rough seas.
What things actually cost
banh mi
1 EUR
iced milk coffee
1 EUR
mi quang noodle bowl
1.50 EUR
Grab ride across town
2 EUR
local beer at a restaurant
0.90 EUR
one-hour massage
10 EUR
Eat well for little
Mi quang (turmeric noodles, the local dish) at Mi Quang Ba Mua - about 1.50 EUR
Banh mi from a street cart - about 1 EUR
Bun cha ca (fish cake noodle soup) near the beach - about 1.50 EUR
Fresh seafood chosen from tanks on the Vo Nguyen Giap beach road - about 8-12 EUR per person
Ca phe sua da (iced milk coffee) at a local cafe - about 1 EUR
Money mistakes to avoid
Using street taxis with rigged meters - take Grab (car or bike), it is cheap and price-fixed
Visiting Ba Na Hills on a weekend - the Golden Bridge disappears behind crowds; go early on a weekday
Expecting beach weather in October-December - it is the rainy season with rough seas; come February-August for swimming
Treating Hoi An as a two-hour stop - stay for the evening when the lanterns come on and day-tour buses leave
Transport without the tourist tax
The airport sits 15 minutes from the centre; a Grab car costs about 3-4 EUR. In town, Grab bikes cost 1-2 EUR per hop, and a rented scooter runs about 5 EUR per day; there is no metro and buses are impractical for visitors.