Turkish Airlines serves the airport of Dalaman (DLM), 120 km away from Marmaris, with daily flights from Istanbul. Many tourists arrive with chapter flights from all over Europe, especially in the summer months. There are buses that connect the airport with Marmaris.
But Turkey has an excellent bus network so you can easily reach Marmaris from many other cities across the mainland. The bus station is at the northeast part of the town, 20’ walking from the Marina but better take a taxi. There are several bus companies, just go there at ask for timetables and prices. The companies have more or less the same prices but not the same services. My favorite is Pamukalle, an excellent company with modern buses, polite stuff, free tea/coffee and biscuits (!) for journeys that last more than 3 hours!
Marmaris-Bodrum costs 15 TL (9euro) and takes 3,5 hours
Marmaris-Izmir costs 22TL (13 euro) and takes 4,5 hours
I took the Pamukkale bus from Antalya for 25 Lira one way. The Pamukkale offýce in Antalya is a bit outside of Kaleici (the old town), but not far from the clock tower. Some Turkish girls Ý asked adopted me and asked around. They might ask for 27 at the otogar--some other Turkish people paid that, but I ýnsisted. (Maybe because I showed my ýsýc card--but the lady at Pamuk. dýdn't speak English so I don't know) There is a free shuttle to the ottogar one hour before the bus leaves--be there EARLÝER than that. From Marmaris otogar there was also a shuttle ýnto town, otherwýse they have dolmus vans for 1 Lýra.
One day ýn advance the bus I wanted to take--daytýme--was already booked out, so keep heed of that when you need to make your way back to your airport!