Here's their data for Fethiye specifically:
https://www.numbeo.com/cost-of-living/in/Fethiye-TurkeyWe rarely venture down to Fethiye now, my OH was there last year and its been three years since I was there (I never get past Istanbul!), so can't comment on local prices as they are now. However, after many years of spending time in both Istanbul and Fethiye, my view is that Fethiye is a pretty expensive area to live, within Turkey.
Compared to our local area in Istanbul, things like taxis, eating out, takeaways, alcohol etc were all more expensive. Food shopping was much of a muchness, local markets had similar produce, at similar prices and Migros was simply Migros.
Rents and property prices are a lot cheaper in many areas of Istanbul, just as they are a lot higher in others.
JF