we have been for the past couple of years, but further south than Marmaris. last time we went to ephesis and would 110% recommend hiring a guide (official inside the fence!) to take you around. Ours was fab. Don't get any suposed taxis or guides that will try to pick you up where you leave your car. take plenty of water about 2l each. It wasn't that expensive but I can't remember exactly what it was. Also if you are driving you must visit mary magadelans place which is only a couple of miles drive away from it. Last year we went to PAMMUCALE and i loved it. We did the white bit, and then paid less than the 40TL to go in and swim with the sunken artifacts in the sulphurous pools. There is an amphitheatre behind it to which is well worth going to. 5tl I think to get in, oh yes it was 5tl each to get into pammucale. you can park quite close to the entrance, but its 1/2 mile walk to get to it from there. Take waterproof beach shoes or flip flops to as you have to take your shoes off for the white bit and the rest is hard on bare feet.
hope you have a great time! wish it was me!