It's been a long time since we did it but we took a Dolmus to the bus terminus at
Marmaris then a bus to Ortaca, from Ortaca you can get a bus or Dolmus to Dalyan, from what I remember it took around 2 hours for the whole journey, no idea what the prices are these days but it was pretty cheap and I can't really see it being less so now
We made the mistake of leaving it too late to get the bus home so found a Pansiyon for the night, not exactly in our planned itinerary but had a great night out, we caused quite a stir at our apartments though, we arrived back at noon the following day and they were on the verge of starting a search party, Oops
I'm sure others will be along with more up to date advice if I'm wrong.............