Is it not a fixed price from Dalaman airport ?
I know airportconnex, united blue do £10 each way for shuttles from dalaman to dalyan, try them, you can book online. Also sure there will be a local bus to Dalyan?
I think you mean the Havas (or service bus) which meets the incoming THY Istanbul flight and during the summer, the other carriers who fly into DLM domestic. 20TL per head to Fethiye and 25TL to Marmaris.Local buses apparently go from the Domestic Terminal to several areas too also for peanuts!!