Arriving in Phuket during high season means higher hotel rates; same as any other destination in the world. Now that Thailand gets 22 million tourists visits per year, if your traveling during high season, booking in advance is your best bet. Worry not, Phuket has a total hotel inventory of 50,000 rooms now and they are all on Agoda.com What I really mean by booking in advance is, you should have your first 2 or 3 days planned out. Best way to do that is book a tour on TourChoice.com. It will often include pick up at the airport, saving you the expense. Consider a 2 day kayaking adventure or 4 day sailing trip visiting all the local islands. Reason I say this is because after you leave the airport, en route to your resort in a taxi or rental car, chances are you will be stuck in a traffic jam for a while. Worry not, it gets better. The once quaint Patong Beach is now more like a 24/7 carnival and that is a serious understatement. So you may want to avoid Patong unless your looking to party party party. Personally, I find Rawai Beach, Kata Beach, Karon Beach and Nai Harn Beach much more to my liking. These beaches, especially Nai Harn provide a quaint and more quiet get-a-way which also have trees close enough to the shore so that if you want some shade, its quick and easy to find.
Phuket also has the most expensive taxis in Thailand. In fact, they are almost on par with taxis in western countries. So if you are planning on being highly mobile while you are here you might be better off renting a car for about 1,300 Thai Baht per day or $40USD. There are good reasons to be mobile, take a 2 hour drive to Krabi or see Old Phuket town. Then again your best option is probably to rent motor bikes for 250 Thai Baht per day, at under $10USD, they go 50 kph, their automatic, very easy to drive and a lot of fun.