I would suggest to rent your car from known companies in order not to experience any problems.
Some of the known companies are: Hertz, Sixt, Avis and Budget.
These have offices nearly in every airpot in Turkey.
For example, a new model of Peugeot 301 or Hyundai Accent Blue is daily 70 Turkish Liras which makes about 30 Euros (SIXT). Even here this price is very reasonable.
Here are the Car rental web pages for Dalaman Airport:
BUDGET: http://www.budget.com.tr/car-hire/Dalaman-Arac-Kiralama-Budget.htm (Click th top right corner for changing language)
Have a nice trip,
sas about 5 years ago