The most I've spent acquiring a cat was just a couple of bucks for an adoption fee.
It's everything that comes after the adoption that adds up. Shots, spaying, and other vet expenses came into play right away. The cost of food has been much higher than anticipated because it wasn't until after I got my cats that I learned about proper nutrition. Litter costs are next to nothing, since I just buy the cheap stuff anyway. (The cats could care less, so why should I?)