I had my cats done against everything, but I remember one of our cats when I was younger having leukemia so I guess thats why. When you book in for your cat to be netered it will have to have a pre-op check and they will probaly give the first injection then , thats what they did with mine. Then you go back in 3 weeks for the next one, and they can go out a week later. The injections cost me about £90 (times 3!!) the girls to be done was about £80 and for the boy to be neutered it was cheaper, about £60.
Have a look if there are any cat charity's around you, they can give you vouchers to use at the vets and you can get up to half price off. I would get him done for leukemia aswell, if you didnt and he got it you would feel guilty.
I sound like a crazy cat woman now don't I?? lol