Went for the 3 hour Phang Nga tour, which was quoted at 4,200 baht. Bargained at the counter (you should get 3,500 to 3,600 baht).
The trip was absolute fun. You get quite thorough training before hand, and guidance along the way as well. Was amazing riding through the river, up the hills, through plantations of coconuts, palm oil trees and banana trees.
The guides were absolutely great and provided us with a lot of insight on the scenery and nature, pointing out trees and what is unique about them.
Join this trip if you want ATV, nature, culture and an EXPERIENCE.
The ATV tour is not available at all tour desks (in fact, less than 20% of them had it in Karon). Be sure to book ATVphuket.com