Tony of Reliable Chimney Sweep at 602-885-1240 just did my chimney for $99, his standard price. (By comparison, a friend who lives just south of Scottsdale Ranch paid $180 to have hers done.) Mine hadn't been done in 22 years and half of the hearth ended up filled with creosote even though I only use it a few times each winter. He is licensed and bonded and came within three days of my calling him. I originally got him off Yelp where he had a five star review. I can't recommend him strongly enough. His recommendation is that it should be done every time you have used the equivalent of two cords of wood.