Ebooks.com has some strange marketing.
"Hey, this ebook on your wishlist? It's on sale! Instead of €25,11, it's now €18,08!
Oh, and here's a coupon for 20% off of that.
I only clicked through accidentally, but the actual price was €8,25.
The coupon worked.
So, right around €6 for "Colossus: The Secrets of Bletchley Park's Codebreaking Computers" from Oxford University Press.
Yeah, I bought it. I've been looking for decent Bletchley books.