I came across this site on reddit and used it for getting my textbook as I couldnt find it anywhere else for cheap. Saved good money. Bought 1 more as well then. Had a small issue (was getting a downloading error) so I emailed them and the issue was sorted out quickly:)
Edit: Apparently the website has moved to https://college.bz/
Answer: Much cheaper, plus it had some good reviews on trustpilot and reddit