Went to Olu Deniz a couple of years ago, its in a beatiful spot. We didn't hire a car, its easy and quite cheap to hop on the bus (dolmus) to get up and down the coast, but I suppose it depends on how far you want to travel.
We did several trips and enjoyed them all. Saklikent gorge is pretty spectacular, but be aware of the young boys who grab your hand to help you wade across the river, they do expect payment!
The natural mud baths are a great laugh although very smelly, and don't wear your best swim stuff!
The abandoned village of Kayakou (not sure of spelling) is worth a look round, we walked there from Olu Deniz, but it was quite a trek. If you like walking though i'd recommend you do a bit of the Lycian Way, it starts up the hill from the resort and the views back over the lagoon are spectacular. Might be too hot in August for too much walking though.
Don't use your rep to book trips, there are plenty of local travel agents who tend to be cheaper.
The boat trips from the beach are good value, the touts will try and sell you a trip as you leave the beach, if you seem reluctant to book they may reduce the price.
As for the bars and shops, they were pretty reasonable when we went, but I read the other day that prices in Turkey have risen by as much as 40% recently, as the shop and bar owners are taking advantage of the increase in tourists avoiding the eurozone.
Finally, if you've not done it before, try a turkish bath, I was so relaxed afterwards I felt like my legs had turned to marshmallow!
Have fun!