How do you go about finding stuff out?

I have very little info even on my grandparents. Name/Surname/Maiden name .... little more.

I’ve checked the GRO registers online for births/deaths/marriages but it doesn’t give you a whole lot to go on. You end up having to do a lot of guess work.

The GRO will send you certs but they are a tenner each so for every generation I’d end up spending twice as much as the previous, which to get anything resembling “a tree” would mean potentially forking out a months wages.

Are there any cheapy workarounds or resources that are dependable but not expensive?