Pamukkale do direct buses from
Marmaris to Fethiye - I think they are either once or twice daily, take around three hours and cost 30TL. You can get more information from their website -
www.pamukkale.com.trIt might be an idea to go to the otogar (bus station) in Marmaris beforehand and check out the timetables etc. There is a Pamukkale office there and the staff are very helpful. They will keep you right. There are other bus services too, but you might have to change in Koycegiz or Dalaman, so that would take longer.