My cat was very cheap initially--$60 to a local cat rescue.
Within a couple of weeks, we spent over $1000 in vet bills because our new kitty had severe constipation. Those were some extremely expensive enemas. We also had another vet visit because it turned out our kitty develops lesions on her face when it gets too warm.
So our cat has some special needs, but her food (2 cases of Wellness canned cat food), a cat laxative given in her food daily, and a big can of pumpkin that we stir into her food, comes to about $85 per month. I buy her food from
Amazon because it's cheaper than the local pet stores. We don't feed any grain based foods and no dry food because of her health problems, but I agree with the poster who said dry (and grain) are recipes for future health issues in a cat.
I realize most cats are cheaper, but keep this in mind--if you get a rescue cat, why is it there? I'm pretty sure my cat was there because she has issues. She was even bald when I got her. I thought it was because her previous owners didn't brush her, but now I realize they may have tried to give her medicine and "missed" enough to have matting from the medicine on her fur. It took me over a week to figure out I could put it in her food since I only feed her canned.