There are lots of options available in Phuket. But for the more popular hotels and resorts in the better locations you should book at least a couple months in advance during high season (Nov-May). The cheapest air-con room rates start at around 1,000 baht in beach locations or 500 baht away from the beach, with proper resorts starting just under 3,000 baht and up. The best rates are usually found on-line and many hotels offer best rate guarantees when you book direct. Most of the time you will pay more if you walk in and take the rack-rate.
There are 5 main areas for tourists to stay in Phuket. Patong is the most popular due to its active nightlife, street markets and calm water beaches however this area isn’t for everyone (especially people with families). The quieter areas include Kata, Karon, Rawai and Nai Yang, all with great markets and quieter beach areas.