We like Sixt. They offer special discounts, depending on the time of year, but shop around to find the best rental car rates in Turkey from the several car rental companies including Hertz, Avis, Alamo, Budget, Dollar, Sixt, Thrifty and Europcar. Most will let you pick up your rental car at Bodrum Milas Airport, Antalya Airport, Istanbul, Adana Airport, Istanbul, Ankara, Kayseri, Izmir
http://www.sixt.com/
http://www.sixt.com/