Well, I took my cat to the vet about three and a half weeks ago for her annual checkup. Said checkup cost about USD 125 (I think that I have a breakdown of that, if you want it), and included one vaccination. The checkup also revealed that she had two broken teeth, and one that was so rotten that it might break off at any minute. So, she went back next week to have all extracted, at an additional cost of USD 150.
I don’t know how much a spay operation is (my cat was abandoned, and was thus spayed long before we got her). My WAG is about USD 75-150; Michi probably has more accurate information than do I.
Feeding a cat costs about USD 0.25 - 0.50 daily, depending on the quality and amount of food. Dry food is cheaper than canned food of the same quality, but of course necessitates a higher water consumption. If you have heavily chlorinated tap water, your cat may refuse to drink it, and require bottled water (I do, and my cat does).
I strongly recommended against having your (hypothetical) cat declawed. If you have a one-cat household, it is totally unnecessary.
If the cat is spayed (or neutered) at a young age, it is unlikely to spray, especially if it is the only cat. Clawing the furniture will not be a significant problem. Get (or make) it a scratching post, and spend the money on a sturdy one; a cat will not use a post that wobbles if it brushes against it.
Cats do shed. Of course, so do dogs. Brush it (depending on the length of the coat) between daily and weekly, and hairballs and cat fur on the rug will not be a problem.
I recommend getting a cat from your local shelter. The cat will probably have a better personality, and the “basic maintenance” (spaying/neutering, vaccinations) will have been done or will be done, sometimes at a reduced rate. An improperly spayed female will have less of a chance of spraying than an improperly castrated male, but a properly neutered animal will have less chance than either. Fancy cats will seldom show up in a shelter, and probably aren’t worth the extra money.
You may wish to look at the VetInfo site (http://www.vetinfo.com/; I’m having bad luck with URLs today), as well as the Purina Cat Info site. Remember that the VetInfo site gives pretty much everything that can go wrong with a cat, and may be a little alarming.