Most of what you need will be available in the library. Sometimes the most popular/most recommended textbook might be hard to get, especially near the exam period, but in my experience, it doesn't make a lot of difference most of the time if you take out a different edition or choose a closely related textbook.
I've had a few times where there's been a book I'd like to get out which I haven't been able to get hold of (like sometimes lecturers recommend a book where there's like 4 copies across all the libraries and about 50 people on the module) but it's never been essential.
I did buy some textbooks in first year that came to about £100, but that was mostly because I was too lazy to figure out the library system, and I bought one last year that was about £40 because the lecturer said it was essential, but tbh I don't think we used it that much and there were probably equally good books in the library, so I didn't really need to buy any of them...