If you need a haircut in Krabi Town, I can recommend Tak Salon (ตั๊ก ซาลอน) on Utarakit Road about 200 meters from the Crab Statue. They might be slightly more expensive than a random salon in Thailand, but the guy who cut my hair was really good. He also styled my hair just the way I wanted it. And how much did I paid? 300 Baht (about $8).
You don’t need to make an appointment, just show up when you want your haircut and hopefully, you’ll not have to wait so long. It’s good to take in a photo of the hairstyle you desire, as the barbers English is very limited. I have my wife who speaks Thai, making things easier.