If you ever attempt a cat rescue, be aware that the cat will perceive you as THE ENEMY. Do not expect the cat to welcome your efforts and start purring as he snuggles up to you for the ride down. Instead it will more closely resemble trying to grab hold of a lit string of firecrackers. Be prepared with lots of body armor as well as a sack with drawstring closure in which to place the cat. Otherwise you will be bloody and in much pain.
Newb has it right, I've never seen a cat skeleton in a tree either. But if the owners want you to act, charge heavily for it. Minimum starting point would be $100-$150, more if it's a large or aggressive cat.