I really hope you are kidding but I'm afraid you aren't. This "solution" is just wrong. Does the OP have a right to be VERY upset? Of course, and I would be, too, but it isn't the neighbors' fault any more than it is the OP's. It is quite unreasonable to expect that they pay for the value of the tree and pot - it simply won't happen, nor should it. The OP sprayed a fish-based substance on the plant and it should be no surprise that a cat found this enjoyable. It would be the same thing if you grew a flowering tree and a crow was attracted to the berries and knocked the tree over. S**t happens. No wonder our society is rampant with a "sue first, ask questions later" mentality. Not everything is somebody else's "fault" that they should be expected to pay for.
The OP even said in the post that they regret shouting at the cat. If that hadn't happened its likely the tree wouldn't have fallen. So there is half the blame. If there is willful negligence - the neighbor knocks over a fence, or sprays a weed killer, etc. that kills your bonsai that is entirely different. But in this case the OP is technically just as responsible by making the animal scared and jumping. Stealing the neighbor's pet and covering your tracks (cash purchase - really??) is far worse than the initial infraction. Suck it up, express displeasure to the neighbors and ask them to contain their animal, chalk it up to the fact that the world isn't fair.
It was more of a joke, but reading my post over it didn't come off as one... sorry.
But people need to keep their animals on their own property, no one should have to worry about the neighbors cat or dog on their property. People should keep an animal indoors if it wanders and causes trouble. And I'm not saying to sue the neighbors, but get them to at least apologize, say it won't happen again, and get some of the money they owe. It's impossible to get a person to pay all of it, and it shouldn't even be expected, but they need to feel some of your pain when they fork over a couple hundred bucks. OP said the pot alone was $200, I would be furious. I would need to get something out of them at least.
My neighbor has a couple dogs and a cat, I have a horse and chickens. The neighbors dog comes on my property and terrorizes the horse, the horse has kicked at it a couple times (thankfully, she missed the dog). My neighbor doesn't realize the horse could seriously wound or even kill her dog but she does nothing. We've told her what could happen, but she said we shouldn't have the horse. Her cat killed one of my chickens, shredded it to bits. We brought the dead chicken over to show her, and she still did nothing. People don't take responsibility for their animals, when they should. If her animals are causing trouble she should deal with it. We were living here before her, and it's her animals causing the trouble, not mine. This is all different from a cat killing a tree, but people need to take responsibility for what their animals do.