It depends what you will be buying.
I spend £6 on guinea pig food which lasts me about 2 months.
Then there's hay. I usually get a bag 3.5kg bag from B&M for £3.49 and it lasts me a week but that's with two guinea pigs and three rabbits. I also buy other hays, like Timothy hay and that's around £3 for 1kg and it lasts about a week. I buyother hays too, like readigrass which is around £4 for 1kg. They don't eat a lot of it so we have it for about a month. This month I decided to get them some they hays which added up to about £30 but that's not necessary, I just like to give them variety.
I buy some vegetables every week. I usually get them in offers or on sale but if I can't find any I just go to lidl. I spend about £5 a week on fresh food. I think I would spend more if I didn't live with my parents - they buy a lot of vegetables so my pets always have the leftovers, peelings or just things things we need to use up.
I can't tell you much about bedding because I use fleece. I bought a few cheap blankets for around £3 each and I use our old towels that we don't want anymore under them. The only cost with this is washing.
You don't need to get things like hideys, bottles, bowls & other cage things often unless you want to. Mine have had their stuff for about 3 months but that's because they got a new cage and I bought new things for it. I think everything will be okay for at least a year or until I decide I want to get them new things
There's also other costs like treats & toys. I get them whenever I feel like it but I can't tell you how much I spend on them because I really don't know.
I hope I helped!