I spent way too much on buying books new - I spent around £35-100 per book, and got around eleven books in total...all in the first week
and all new.
My friends managed to get the same books from the book fair/online at around 80% cheaper.
One thing you need to understand is that you'll only need many of the books for one module, or part of one module. The second is that many are available either online via your university library portal or another website and the library will often have physcial copies too.
Check your reading lists as well, as sometimes you'll only need a few chapters from one book, which may cost £55 and be useless after that.
I will never buy another book new for university again. My Economics one was £60 I think, and I never used it once, another module needed two books which totaled £90 and one was used for one week and the other just as further reading. I easily wasted over £600 on text books instead of going to the book fair or buying older editions.
In September I am going to:
-Check what books i'll need to use the most, and buy them second hand
-Check what the library has online before even buying them
-Make the effort to go to the book fair and grab anything remotely relevant for the insanely low prices.