Room rates in Rio de Janeiro have soared even though the Olympics in the Brazilian city are four years off.
UK travellers faced hotel price rises in Rio of 31% in the first six months of this year compared with the same period last year, according to a survey by Hotels.com.
The increase took the average one-night Rio room rate to £182, second only to Monte Carlo (£197) in the list of the world's most expensive hotels.
Muscat (£179), New York (£171) and Moscow (£171) were also particular pricey destinations for Britons in the first half of 2012.
In contrast, a night's stay in Phnom Penh in Cambodia averaged just £35 in the first six months of this year - 12% down on the January-June 2011 period and the destination offering the best-value room rates for Britons.
The next best-value hotels were in Pattaya in Thailand (£47) followed by Hanoi in Vietnam (£48) and Chiang Mai in Thailand (£51).
Of the 10 most-popular city destinations for Britons, six went up in price and four were cheaper than last year.
Of the top 10, hotel rates in Las Vegas rose 15% to an average of £84, while New York (£171) and Stockholm (£129) both rose 7%.
The biggest decrease among the 10 was in Rome where rates fell 10% to £108.
Overall, UK travellers faced price rises in nearly two thirds of the international destinations surveyed.
Hotel rates in the Spanish regions of Benidorm and Alicante fell 8% while Athens rates were down 10% at £72.
Rates in Dubai rose 21% to £134 and Abu Dhabi was up 12% to £113.
Florida rates rose sharply, with Orlando up 27% to £78, Key West up 21% to £159 and Fort Lauderdale increasing 19% to £109.
Although Rio rates rose, prices in Buenos Aires were down 14% at £88.
Hotels.com communications director Alison Couper said: "The news that UK travellers faced a rise in prices at two-thirds of overseas destinations in the first six months of 2012 may appear daunting.
"But our price index makes it easy for those planning trips to look for destinations where they can pick up a bargain and get a maximum return on their travel budget."