asda i get butchers classic £2.78 for six tins wood pellet litter is £3 for a huge bag biscuits feline fayre £2.48 for 2kgs bags i have four adult cats and two fosters kits at the moment and food and litter costs me around £10-£12 a week at the moment flea treatment i buy the big spray bottle of frontline its £30 but lasts a whole year worm tablets i buy milbemax from vets and they work out around £3.50 each
Pet Supermarket does cheap(er) wood-pellet litter - have just ordered the Mayfield one, having previously had the Snowflake & Pettex ones - I get the huge 30L bags.
Food I order in bulk from Zooplus - they often run special offers on things (invariably just after I do an order, of course...) which brings the cost down further. I belong to their money-off scheme too: made the cost of joining back on my first order, pretty much!
Mine like the wood pellet stuff pets at home do, I'll have to source the cheapest version. Thankfully we normally have an unused tray in the corner for emergencies only so once Tortiecat's skin has healed up and she can go out again I won't need much litter.
Flea and worming from the vets - to be honest they usually are just the same cost as online. I get food and litter from zooplus, especially the bulk stuff as it works out cheaper in the long run. I have two cats and do a zooplus shop every two months.
I get flea and worm meds from the vet - they try to be very reasonable on other costs so I don't mind if they make a couple of quid there. (Although I don't think they make much.) And I know the meds are pukka.
As to food - you're on your own I'm afraid. Seniorboy is very fussy (privileges of age) and eats better than I do - and certainly much more expensively on a pound for pound basis.