Accommodation is relatively expensive. Doubles range from 400 baht up into the thousands the closer you get to the beach front. If you are on a budget expect to work hard to find a decent price. If you get really desperate, a couple of places rent out tents for about 200–300 baht. One thing to note, prices are double during the high season which runs from Oct-Nov until May. Other times of year you can find relatively cheap accommodation in the 200-300 baht range.
To have the best choice of accommodation, arrive in Phi Phi just before the Full Moon Party, when most people will be on Ko Pha Ngan. Since a lot of people move from Pha Ngan to Phi Phi after the party, accommodation may be very hard to find on Phi Phi around this time. It is not uncommon to see people arrive on the morning ferry only to leave on the afternoon one because they have been unsuccessful in finding accommodation.