Luckily a lot of great helpful resources are online, so using websites/online resources like PMT, MME revise, past papers/mark schemes/examiner reports, specifications, save my exams, freescienclessons, GCSE maths tutor + exam Q for example can help you a lot with revision; so revision guides/workbooks aren't 100% essential if you're looking to save money.
I'd say get the cgp combined science practice workbook as you don't need the separate books if you're not doing triple science and that workbook has a lot of good practice questions with answers too. Like this one:
https://www.cgpbooks.co.uk/secondary-books/gcse/science/combined-science/sahq42b-gcse-combined-science-aqa-exam For maths, most of the revision lies within understanding (which you can get from a youtube video explanation) and practice (where there are plenty of questions online), so unless if you specifically struggle with maths, you don't really need a workbook or revision guide for it.
For english lit, you can get revision guides from either cgp or york notes for the specific text you're doing (like an inspector calls for example) - I highly recommend the channel glow up your grades for english lit and language as it helps me a lot.
For english language, it's mainly a skill, but if you want a revision guide for it, then the cgp one is quite helpful; but for english overall, I think the workbooks are a bit of a waste of money:
https://www.cgpbooks.co.uk/secondary-books/gcse/english/english-lang/enar42-gcse-english-language-aqa-revisionFor other subjects, if you need more practice questions like for geography for example, then you can get the workbook if you think it will help. Or if you want something to help you in making notes with some practice questions here and there, you can get the complete revision guide + practice books from cgp.
I hope that helps a bit!