As someone else said, yep they need taurine, so people food isn't an option other than for treats. I kind of liked the idea of fish, but as a rare treat, maybe to lure the cat into the carrier to be taken on trips to the vet, for folks that have trouble with that. I used to have a cat like that. I have one cat now, but have had multiple cats in the past and it does get pricy. I'll happily share the little I've learned over the years. One is that I buy a fairly good quality dry food, a hairball formula. I tried the hairball remedy gel years ago and it wasn't effective at prevention, it just brought them up then, to be dealt with at that time. The dry food hairball formula we use is a preventative, that allows the hairball to be broken up and go the other direction, as it were :) So that's a bit of savings there. If I were going to use something like that instead of a hairball formula food, I would use something much less expensive. According to the ingredients it is flavored petroleum jelly. I didn't like the idea of giving my cat that once I read it, so would give the cat a bit of oil from a can of oil packed tuna, instead.
Also, we dont buy enzyme cleaner now because she never brings up hairballs anymore since we switched. We used to have to deal with them once or twice a week, so we're saving that cleaner plus the paper towels used on them.
Another benefit to the decent quality dry food is the waste is much smaller, so we use less cat litter.
I'm not saying dry is better than wet. Wet may be better for some, but this has worked out well for us. Also, she hasn't had any stomach upset and no mess of that kind to deal with since we switched.
When we used a pretty cheap food many years ago with another cat, we had to take her to get her glands expressed regularly, and the vet kept telling me it was the poor quality of food, but I didn't listen. He said that isn't needed with cats on a good diet. I finally listened!
Hope this helps, my heart goes out to anyone who gives a home to fur-babies :)