The average daily cost in Hoi An is calculated at £67.78 ($74.19), a drop of 10% against 2019, in the latest annual Holiday Money report released by the Post Office, the U.K.'s leading currency exchange agency.
This is cheaper than Cape Town in South Africa (£68.49) and Mombasa in Kenya (£77.41).
Japan's Tokyo ranked fourth on the list with an average cost of £81.63, followed by Indonesia's Bali (£82.40).
The rest of the top 10 were Phuket in Thailand, Rio in Brazil, Montego Bay in Jamaica, Orlando in the U.S. and Penang in Malaysia.
Tourists' living costs is based on the minimum required budget for eight staple items that holidaymakers are likely to purchase – a cup of coffee, a pint of beer, a can/bottle of Coca-Cola, a bottle of water, sun cream, insect repellent and a three-course dinner for two with a bottle of wine.
"Vietnam's Hoi An has recorded price falls that outweigh the impact of a stronger Vietnam dong against the pound, placing it in pole position," the report said.
The report's barometer table is compiled from a combination of data supplied by the long haul specialist Travelbag and cross-referenced with prices provided by national or regional tourist offices of participating countries.
The ancient town of Hoi An, much loved for its peaceful atmosphere and its centuries-old houses and pagodas, has repeatedly featured in best-value destination lists over many years now.