KTEL Santorini Buses has a good website with schedules and prices. Tickets are purchased on the bus.
In summer buses leave Fira regularly for Oia, with more services pre-sunset (€1.80). There are also numerous daily departures for Akrotiri (€1.80), Kamari (€1.80), Perissa and Perivolos Beach (€2.40), and a few to Monolithos (€1.80).
Buses leave Fira for the port of Athinios (€2.30, 30 minutes) a half-dozen times per day, but it’s wise to check times in advance. Buses for Fira meet all ferries, even late at night.
Car & Motorcycle
A car is the best way to explore the island during high season, when buses are intolerably overcrowded and you’ll be lucky to get on one at all. Be very patient and cautious when driving – the narrow roads and heavy traffic, especially in and around Fira, can be a nightmare.
There are representatives of all the major international car-hire outfits, plus dozens of local operators in all tourist areas. A good local hire outfit is Damigos Rent a Car. You’ll pay from around €50 per day for a car and €25/30 for a scooter/four-wheeler in high season, but it pays to shop around. Note: scooter hire requires you to have a motorbike licence, while four-wheelers require just a car licence. Check this website for details: www.santorini.com/rentals/motorbikes.
Fira’s taxi stand is on Dekigala just around the corner from the bus station. A taxi from the port of Athinios to Fira costs €10 to €15, and a trip from Fira to Oia about €15. Expect to add €2 if the taxi is booked ahead or if you have luggage. A taxi to Kamari is about €15, to Perissa €18 and to Ancient Thira about €25 one-way.
Santorini Transport is a good option for arranging fixed-price transfers to/from the airport or Athinios port.