If you don't have a transfer arranged, your best bet is a metered taxi. To find it, turn right straight out of the doors and push through both the humidity* and the taxi touts. The rank is a small building with a green sign at the end of the terminal.
A metered cab should cost no more than 500B to Kata, which includes the 100B airport levy. The touts charge 650 and up as well as their additional scams. "Limousine" taxis are nothing more than a Honda Civic with leather seats.
The trip will take 50-60 minutes to Kata - much longer than the distance on the map would suggest. Major roads in Phuket are both congested and chaotic!
*Off topic - don't be put off by the staggering wall of humidity you walk into as you exit the terminal. It is much better on the beaches.