There are several companies serving that route and they run about every hour. Look out for companies running buses to Malatya, Van, Konya, Sivas etc as well as those just showing Antalya as a destination, most of them go via Antalya. It'll cost you between 18 and 25 TL per person eachway depending on the company.
Just be careful though that you don't get one of the services that goes via Kalkan and Kas because, although it's a very scenic route, it'll add about 2 hours to the journey.
CG. If to you take Pamukkale, they will take you from the Otogar on a sevice bus to Örnekköy where Hotel Sera is.There is no charge for this just ask at the Otogar when you arrive.All the other Bus Co's do the same so not a problem. If you need any more info just ask.