This depends on what stage of guinea pig ownership that you’re currently at. If you’ve only just decided to take care of some guinea pigs then you’ll need to buy some things to get yourself set up (such as a hutch) whereas if you’ve been keeping guinea pigs for a while then you’ll have all the equipment needed to take care of them.
Guinea pigs really enjoy fresh vegetables in addition to their dry food
Once you’ve bought the hutch and run, you’ll need to buy food bowls and water bottles. If you buy an Eglu Go Guinea Pig Hutch then these items come free with the unit, but otherwise you’ll probably need to buy these from your local pet shop. Next you’ll regularly need some newspaper, and some hay for bedding. Depending on what hay you get (guinea pigs need hay rather than straw, as straw is very thick, scratchy and can damage their eyes) it’ll be two or three pounds for a decent bag. Food (the dry cereal and the fresh vegetables) will cost about four pounds per week as well. So in general running costs for two or three guinea pigs will only be about six or seven pounds a week, and less in the summer than in the winter, when they don’t need quite as much hay to keep warm!