I guess you aren't planning on spending any time in Istanbul are you?So you could look for a connecting flight upon arrival and fly directly down to Izmir and stay in Selçuk Sunday and Monday evenings.THY,Anadolujet,Pegasus,Atlasjet and Onurair all cover the route.The latter two carriers also include an airport transfer bus to Selçuk in the ticket price so you have no hassles getting there.If you do this then be sure to allow a very clear 3 hours between landing and take off times.
Monday morning go to visit Ephesus and in the afternoon enjoy all the other historical attractions Selçuk has to offer,not least the recently reopened superb Ephesus Museum in the town centre.Pretty much every hotel there is happy to take guests down to the site for free if guests ask.
Tuesday morning you can then take the bus down to Marmaris.To do this firstly take the local bus for the 1 hour run to AYDIN,a main transport hub town.From there Kamil Koç Turizm have regular buses to Marmaris.
These are the bus times from Selçuk;see the RH column headed Aydın sub head Selçuk'tan ,first one at 07.00 but you can take the 09.20 one-
At 11.00 Kamil Koç depart Aydın arriving in Marmaris at 13.45,cost is 30TL.
Marmaris otogar it to the north of the town centre but there are shuttle buses to take you there and I seem to remember one of them goes close to the ferry port but ask the driver-or take a taxi if you have a lot of luggage.