I love to find books at discount prices and have a few favorite locations for doing just that.
I found The Republic of Thieves at Goodwill for under $2.
I ordered Changeless from Amazon using points that I had built up so it was, essentially, free.
I found all of the books listed below at Salvation Army for $0.69 each.
And last but not least my favorite used book store, Half Price Books. Where all of the books are, as the name suggests, half off the cover price, sometimes even lower. A few of these books were even on clearance for $1 and $2.