you sound very like the memsahib and I!
They did a bit of a double take when I took the car I had rented back
and they saw the mileage!
Do consider that although car hire is not horrendously expensive in Turkey Petrol is, so, go for a diesel if you are going to drive a long way. Much as I love Calis/Fethiye if I was coming to Turkey for a week and particularly wanted to see Ephesus, Pammukale etc. by drivingt myself I would probably head further away toward Bodrum/Izmir regions as it will be a very long drive! I drove from Calis through to Side and back in one day and it was exhausting! In fact I cancelled any thoughts of driving to Ephesus! There are good value trips from Calis by Bus and staying overnight though.
There is so much to see and do around Calis that you can easily get to by car, Tlos is a fascinating Site, I would highly recommend an reasonably early start to Tlos, (not that far, about 40 minutes from memory) pay a guide ---- worth it -- and then a trout Lunch at the original Yakapark further up the Mountain, amazing views! A walk down the Sahklikent Gorge is amazing, the beaches like Ptara and Iztuzu are World class. A walk though the ghostly ruins of Kaya Koyu and a swim at Gemiler etc. Car Hire is all much thge same to be honest, I used Fethiye Renta-car just opposite the PTT and it was excellent, I have used 2 others that were ok! What I did like about these guys is that they did total insurance includeing HDW whihc most wont!
Enjoy Calis!
Meldrew