If you get off in Oia, you can pay 5 euro for a trip by donkey :). There's a loong way up to the village.
The Volcano is sleeping, so you can visit it anytime. Besides what you pay for the trip there's also a 2 euro fee, a sort of Natural Park entrance fee. All the boats that arrive on the island have a guide that speaks several languages. He'll take you up and explain things. You should wear some confortable sandals or snickers. The are is rocky.
The stop for lunch is in Thirassia, an island close by. there are some tavernas there that serve all sorts of sea food. The donkeys are ready to get you up in you're ready to explore the village.
The ferry that connects Crete and other island to Santorini. Megajet. Roundtrip to Crete is 90 euro/person.
Oia in the distance
Donkeys on Thirassia
By donkey up to Oia
A cruise ship waiting for the tourits to get back from their visit on the island