We just spent a ridiculous amount of money having our two cats spayed, micro-chipped, and tested for feline leukemia and feline AIDS, but that's mostly because I was paranoid and had the pre-anesthesia blood tests done. I think the surgery itself was around £50 per cat, and the blood tests were £100 per cat. Mine were both in heat when they were spayed, so I didn't mind paying a bit more. I'm not really bothered by vet bills, though, and consider anything that keeps my cats healthy a bargain, no matter what the price.