It may be possible for you to get the ferry from Bodrum to Datca and then you could do your stay the other way round. When you have finished with Datca you then get a bus to Marmaris and then to Turunc. However during September and especially during stormy weather the frequency of the Bodrum to Datca ferry decreases and is not necessarily daily. You may be able to find the timetable nearer the time but they do cancel them in bad weather.

Icmeler on line do direct transfers to marmaris,turunc and icmeler from Bodrum airport I have no idea how much they cost but if you google icmeler on line it is all on the website

You may take the HAVAS Airport Shuttle Bus at the Bodrum Airport which may take you to Bodrum Bus Terminal, about 18 lira per 1 person. There you may easily find a bus for Marmaris. See HAVAS services from http://www.havas.net/en/shuttle-parking/bodrum/

Thanks everyone for your suggestions.

Regarding doing the trip the other way round, I would rather to the hardest part first then we know it is a simple hop back to Bodrum airport to ensure we don't miss our flight, we have now booked both the Turunc and Turgutreis accommodation.

One way airport transfer is £65 which I suppose is not bad for the distance involved, it is our last resort I guess, at least it will be the quickest way.

We did consider going to Bodrum using Resorthoppa as it is cheaper than the Havas bus but it means us going away from our destination, thus wasting time, and I know there are fewer buses towards Marmaris in the late afternoon, frequency unknown.

Just an update on the above trip and transfers we used for future reference.
We eventually ditched the idea of car hire/using bus and dolmus to get to Turunc from Bodrum airport and went for a private transfer which we would fully recommend. There were a lot of road works and I am glad that I was not behind the wheel as it was a bit hairy in places when someone overtook in a totally inappropriate place and with something coming the other way. Our transfer was with Folo Travel (the company used by Icmeler on line), we were contacted to confirm the day before we left the UK. The driver was there waiting for us, displaying a large clear board with my name, took the cases and stored them in the boot of the spacious car, he was very courteous, helpful (stopped for water for us and to take a photo) and an excellent driver and I wouldn't hesitate to use them again and the cost? just £55.
http://www.transferonly.co.uk/
We used the taxi boat from Turunc to Marmaris and walked up to the Pamukkale bus company's office at the Tansas shopping centre from where the bus company offers a courtesy bus to the main otogar where you can catch the bus to Datca. The journey was fabulous, so scenic, it was worth the 12YTL just for the view, the whole day's journey was very enjoyable.
From Datca we caught the courtesy bus from the ferry office to the harbour and the ferry over to Bodrum harbour from where we walked up to the dolmus station and took a dolmus to Turgutreis. No problem with the luggage, the driver put it in the boot. The whole trip went very smoothly and we arrived in Turgutreis around lunchtime.
We used Resorthoppa from the hotel back to the airport. We would certainly use Bodrum airport again flying EasyJet from our local airport.

I'm glad to hear your trip went well. I quite often fly into/out of Bodrum with Easyjet from my local airport if the prices/times are right and then get the ferry to Datca. It is a nice trip and for me preferable to a road trip. Sometimes we have a stop over in Bodrum which also makes a nice change.

Glad your trip went well. I would second that about the journey from Turunc to Datca being very enjoyable. A few years ago, when on holiday in Turunc we spent a night in Datca, travelling by public transport via the same route as Scousemouse. It's quite easy to travel around in Turkey by public transport which seems to be remarkably reliable. For anyone staying in Turunc, Icmeler or Marmaris a night or two in Datca makes a pleasant change of scenery and the bus ride from Marmaris to Datca is well worth doing, where you notice the landscape changing quite dramatically. We found it quite easy to get accommodation without prior arrangement and would thoroughly recommend the trip!