I'm not sure how much difference having a pedigree cat will make price-wise, but it will only really effect insurance.
I have two moggies and I spend:
£12-15 for a 3kg bag of Iams dry food every three to four weeks (it's normally on offer somewhere), there is cheaper food but my cats were bottle-fed as kittens and have very sensitive tummies, and Iams is the only one I've found that they get on with.
Another £12-£15 for four or five boxes of Whiskas pouches, they have one each a day, again it's usually on offer somewhere if you shop around.
A bag of value cat litter costs about £1.50, and I can change two litter trays twice with a bit left over, or three times at a stretch. And a bottle of value disinfectant for cleaning them out, about 50p. That's about every two weeks. Some cats don't like certain types of litter though so if yours don't take to the value litter you might have to pay a bit more.
Treats and toys and stuff - mine like Dreamies which are about £1 a bag, but they don't eat many because it gives them the runs. They also go mad for these little ping pong balls with feathers on, which luckily only cost 15p each.
And their insurance is about £16 a month, it's slightly more for my male cat than my female. Both are neutered and chipped.
I think that's about it for day-to-day stuff, obviously you'll have to get a litter tray, scoop, blankets, collars, brushes, bowls etc as well. It comes to about £35-40 a month altogether, but obviously that's for two cats not one.