Lift or Scaffold
It is somewhat alarming to me that anyone with the means can rent a towable boom lift for work at height, but these are indeed available for those who are so inclined. There are dangers to be considered when using this equipment without significant training, so proceed only with a careful mindset. Use of a lift is limited only to those sites where there is enough access to allow the lift to be towed into position, and, of course, you must have the means to tow it. It is also very important that you consider any electrical power lines in the area and stay at least ten feet away from them.
It’s rare that a lift is used as a do-it-yourself solution for a cat rescue, but I know of a few cases where it was done, and it was successful. The advantage it offers is that the cat owner can be the one who retrieves the cat, and the cat is far more likely to be cooperative with the cat owner than a stranger. As with any rescue, it is best to proceed slowly and quietly while talking to the cat in a calm and relaxed voice. If limbs are in your way as you ascend, try bending them out of the way instead of breaking them, because the noise of a snapping limb can make the cat more nervous. If the sight of a carrier does not alarm your cat, then bring a carrier or some other means of securing the cat for descent. If the cat is not secured, he will likely jump to the ground once you get close.
Scaffolding may seem like an odd solution at first, but it can be a viable one in certain cases. It is limited to cases where the cat is not very high, the tree allows enough room for the scaffolding structure, the cat is expected to be cooperative, there is someone capable of building it and climbing it, and there are no power lines close to the tree. For example, if the cat is 20 feet high on the lowest limb of a Pine tree, scaffolding could work well. If the cat is easily spooked or not expected to be friendly to the person who climbs the scaffold, then it’s probably going to be a wasted effort.
Often, the business that rents the scaffolding will also deliver it to your site. Tell them how high you want to go, and they will tell you what you will need and how to build it. It is usually not hard to do. Be sure you can set it on a firm foundation, ideally, next to the trunk of the tree where you can also secure it as you build each section.
Build the scaffold slowly and quietly, because fast movements and loud noises make most cats nervous. You want the cat to be as calm as possible by the time you reach his height. If the cat is nervous, then wait a while to give him some quiet time to calm down before trying to retrieve him.