The rates in the banks are the same as you'd get in Fethiye. If using a döviz, don't use the ones in tourist areas as like in any major city, you're unlikely to get a good rate. Saying that, some of the best rates I've had have been in a little one near the Kapalıçarşı - they're giving 2.7 to the £ just now, don't know how that compares with Fethiye.
JF