Last 3 books I have bought:
LA MONNAIE ET LE PORTRAIT ROYAL: Brussels 1991. Issued by National Bank of Belgium. Book about painters and sculptors who have designed royal portraits on coins and banknotes of Belgium. Some interesting facts, but not very useful for numismatists. But I believe it's worth E 5.- I've paid for it. Available in French and Flamish.
О ЧЕМ РАССКАЗЫВАЮТ МОНЕТЫ: Minsk 1977. Despite on infantil title of the book ("What are coins telling?"), the book is perfect! It contains all the history of money in the territory of Belarus avoiding just coinage of Poland 1923-39. Probably all best numismatic books I have read are in Russian but catalogs. This is the area they have to work yet!
Book has been bought at local antiquity shop for Ls 0.15 (US$ 0.27).
MONEDAS Y BILLETES ESPAÑOLES 1833-2004 Y DE LA UNION EUROPEA: Barcelona 2005. Catalog type book, probably one of the best national catalogs I have seen. Since it was out of date (there's edition 2006 available) I've got it for E 5.-