The Turkish town - which sits on the "Turkish Riviera" in the Mediterranean - has been named the best value holiday resort for families due to there being a 24 percent slump in the Turkish lira against the sterling since summer 2016.
Following behind is Sunny Beach, Bulgaria; Limassol, Cyprus; Crete and Porec, Croatia.
There was only one western European resort to make the list and that was Spain's Costa del Sol, which was much cheaper than the likes of Ibiza, Sorrento and Nice.
The study, which was commissioned by Post Office Travel Money, also found prices fell by 5.4 percent in Crete and 4.6 percent in the Algarve compared to just 0.5 of a percent in both Sunny Beach and the Costa Blanca.
Andrew Brown of Post Office Travel Money said: "The clear message is to plan ahead - pack what you can to avoid forking out cash on basics like suncream and insect repellent and squeeze last year's beach gear for the kids into the suitcase. The Beach Barometer reveals just how much these items can cost - especially in some of Europe's more expensive resorts.
"For those who haven't already booked, it is worth checking what late deals are available to the best value resorts in our survey. Marmaris, Sunny Beach and the Costa del Sol all look good value and the general message is to head east for lower prices.
"With the evidence of overspending revealed by our consumer research, the best advice to families heading overseas is to do their homework on prices and set a realistic budget for the resort they are visiting. Buy currency before leaving home to avoid poor airport bureau rates and take enough to avoid incurring hefty charges for using credit and debit cards abroad."