The Saruhan's nightly 45-minute whirling dervish ceremony is the best one in Cappadocia. You must book ahead – most hotels and travel agencies in Cappadocia can arrange it for you. The price will vary according to transport costs there and back and how much commission your tour agent or hotel is skimming off the top.
Though the setting is extremely atmospheric, the sema (Mevlevi worship ceremony) is nowhere near as impressive as those staged in Konya or Bursa. If you're heading to either of these places, you can give this a miss.