Spaying a cat that isn't your cat

I wish I could do that here. Spaying and neutering costs a lot where I live. If I did this, I would end up in the poor house. There are many stary cats around here and although I think people care, the problem is nobody can afford it. It would cost around $25 per cat and to us that's big. In the vicinity of my house there are at least 15 cats. There are more down the street and even more in other places. I wish the city government would have a budget for this. Perhaps we can just pretend to be the owners of the cats if they would spay for free. The put stray cats to sleep and I can't have that on my conscience.