How many of you travelling I wonder? It may be cheaper to hire a car & drive.
I did this recently, under 3 hours from the airport to Calis going the main road & a nice leisurely 5 hours going back the coast road with a stop off for lunch. Cost of hire car was 100euro (they only took Euros for some strange reason!) & a total of 731klms over my stay cost me 130ytl in diesel.