Cheap new books!!
My OU course next year has three set books, totally Â£66.93 (RRP). There's also a book of essays that comes with the course material, but which was also published publicaly, so you can buy it to read it earlier if you want to, so when you read it during the course it's not your 'first pass' on the content. That costs Â£25.99. So that totals a lovely Â£92.92.
Searching online, Amazon was cheapest for all of them, but even so came to Â£79.37 for all four books (and would have free postage)
So I looked on Amazon marketplace, and eBay, and AbeBooks, etc, and I didn't buy straight away but kept looking every so often for when bargains came up. Today I was despatched the last of these books - I have spent a grand total of Â£36.22 including postage, I have got as-new, clean copies of the three set books; the 'extra' book I have a lightly-pencil-annotated copy, but as I am going to get a brand new copy of my own with the course materials I'm not bothered by that.
Could have been even cheaper if I didn't want unmarked copies, but it seemed like a nice trade-off between spending a fortune and getting good condition books