In Koh Phangan, the Full Moon Party takes takes place in Haad Rin, so it is logically the part of the island where there hotels and guesthouses are the most numerous. Used to receive massive crowd, this is the place in Thailand where tehre are the most multiple-bed rooms. If you plan to come to Koh Phangan for the Full Moon, it is essential to book your room in advance. Hotels and accommodation on the island are literally mobbed. Room rates are often more expensive during the party also. The rest of the time, it is much easier to find a room in Koh Phangan and the island is much quieter. The cheapest guesthouses in Koh Phangan, are in Thong Sala but access to the sea there is not suitable for swimming. There are also some nice and cheap resorts inland. Anyway to enjoy Koh Phangan, rent a scooter but be careful the descending and ascending roads can be very tricky and dangerous especially during the Full Moon Party when you may cross drunk drivers on the road.