Good Deal or Not?

S2 gave me a little catalogue of book titles from his school's book club this morning. I had a quick scan over the titles and thought that there were some really good deals. For example, 20 books of the "Horrible Science" series for less than GBP 20/-.  However, I discovered a separate list of pricing in the local currency. A quick calculation revealed that the school had not used the current exchange rates. Using the same example as above, I would have thought it would work out to be less than USD 35/-. Instead, the list price was almost USD 50. I certainly would not be buying from the school's book club!