Any specific cost figures will be (a) localized and (b) out of date eventually, so I'll address categories more broadly.
Adoption costs: The shelter sets a fee for this, sometimes reducing it for older animals. At least in the US, but I suspect most other places too, the cat will come microchipped, spayed/neutered, and current on vaccines.
Even though the cat is current on vaccines, it's a good idea to take it to a vet for an initial checkup soon after adoption. The shelter I used required this within two weeks. See "vet" below.
Food: This depends on what you feed, both type and brand, of course. To estimate this, look at packages in the store, using the feeding instructions and package size to work out cost/day. Then do the math. My two adult cats go through about a pound of dry food a week (together) plus about 10 cans; your mileage may vary.
In addition to food you will probably want to keep treats on hand. This is a minor addition to the food bill.
Litterboxes and litter: The conventional advice seems to be to have one litterbox per cat plus one more. The box is a one-time expense. The initial filling of litter is more expensive; after that you just need to top off to replace what you scoop out. I go though a 20-pound jug of litter every couple weeks, I think (for two cats).
For both food and litter, you can also ask the shelter for advice on rate of consumption. They have data; I have anecdotes. :-)
Routine vet visits: Plan for an annual checkup and vaccines (twice-annual later in life). A vet can give you prices for this over the phone. Prices vary.
Non-routine medical care: As with people, sometimes stuff happens -- pets get sick, or have accidents, or some emergency comes up. As cats get older the likelihood of conditions requiring medical attention rises. You're adopting a cat for its lifetime, not just its good years, so do plan on this. Unfortunately this is hard to predict; some cats may be fine with regular checkups and others may need a lot more. Once cats reach about ten years old, in my experience vets start recommending twice-annual checkups (no longer just annual) and at-least-annual bloodwork (CBC screen or the like). The latter helps to detect problems like kidney disease or liver disease.
Supplies: You'll want to have a variety of toys (stuffed toys, string toys, balls, etc) on hand. Different cats prefer different types, so don't buy a lot until you find out what your cat likes. These aren't that expensive, and some you can make yourself if you're inclined. Over time they get destroyed and you replace them.
It's important to have things to scratch. Some cats prefer to scratch vertically (scratching posts) and others horizontally (cardboard scratching pads). Don't skimp on a cheap, short scratching post; the cat needs to be able to stretch out. I've found that the ones with sisal rope get more use than the carpet-covered ones, but I don't know if that's common or just my cats. I get about a year out of the cardboard ones before I have to replace them.
Some cats like beds, cat trees, padded window seats, and the like, and others completely ignore them and sleep on your couch (or your bed, or you if you let them). Among the cats I know, the "doughnut" beds seem to be the most popular of these items.
Grooming: Nail clippers, a good brush, and a flea comb are essential.
Carrier: You will need a carrier to transport your cat safely (e.g. to the vet).
Pet-sitting: Cats are creatures of habit so it's much better to have somebody come into your house than for you to board the cat when you travel. Pet-sitters are probably listed in the phone listings, and if your vet offers a bulletin board for ads, business cards, etc you'll find many options there. Prices vary, so shop around. Personally, I prefer to trade cat-sitting services with friends who also have cats; that way I know the people who are coming into my home and all the cats get to know the people involved.
Household wear and tear: Some things are going to get scratched, knocked over, or occasionally soiled. It happens. For the last, the right cleaning products applied promptly should fix it up.