Amazon.com and for you, Amazon.co.uk, look at used/new prices, and ebooks where available; bn.com, for older works, often has super cheap ebooks; don't overlook going off-continent - I'm U.S. and I had a book shipped from Australia for $11 shipping.
Bookfinder.com, aggregates used and new booksellers
Half.com, often contains listings not indexed elsewhere, and also toes into ebay.com listings
---
Those are the most important tips. Other lesser ideas: abe books and powell books are good independent booksellers (used/rare). If you're looking for an obscure title, many larger used book warehouses offer title search for a fee - can turn up things the others don't.
Happy hunting.
![[Image: extraordinarywoo-sig.jpg]](https://i.postimg.cc/zf86M5L7/extraordinarywoo-sig.jpg)