I have a lot of resources of my own that I have collected/created over many years of teaching. If I were to return to tutoring I would use them. I would also buy sample papers of Key Stage whatever you are tutoring to. I did this when tutoring my Grandchildren in KS2 & 3 after Covid to enable them to catch-up. You need to know the standards to which you are tutoring, so I think that these are inescapable.
I can't think of anything that won't cost some money apart from haunting 2nd-hand bookshops etc.. You can find useful educational texts there usually.
Once you know what is expected you can always create your own materials as a lot of us do/did.