$5-10/month on food and litter? Not me!

I buy my cat food at Petco and it usually costs me $13-18/bag. I stopped keeping track of how long it takes us go through it. I alternate cat litter. Sometimes we go through phases where we get the $2.50/bag version and change it out every week. I've gone up to about $20 for a bag/box of litter where I changed it out completely probably once every 3-4 weeks.

Vet appointments aren't often between certain ages but can get pretty darned expensive if you have to have any tests/blood work done.

And probably most of their idiosyncracies/stubborness will end up costing money. Remedies for scratching furniture, going outside of the litter box, eating this or that.