Kitten is free--far too high a supply out there that anybody should pay a dime beyond the previous owner's/shelter's expenses for shots/vet care.
Food is $10-20 per month.
But there's more:
Litterbox, litter, toys, brush/comb, lint roller (for your clothes, not the cat), toenail trimmer: $50
First shots/check-up: $75-100 (many times, the owner of the mother cat has taken care of this, in which case, you would pay that person for vet bills.)
Getting him/her fixed at 6 months to a year old: $100-200 (females are more expensive because the operation is more invasive.)
Yearly shots/check-ups: $50-100
That's for each cat, and yes, I too recommend two cats. (I had just one for awhile--she would destroy things when I wasn't home because she was bored. When I got a second cat, the problem stopped imediately.)