My biggest expenditures for books (paper or ebooks) both cost around $40.00-$45.00 when I got them. One was a brand new copy of the Oxford Shakespeare and the other was a used set of "The Story of Civilization" by Will & Ariel Durant. The Durant's were almost brand new in appearance and each volume brand new cost $25.00-$30.00 so to get the set in such good condition for only $45.00 was a real bargain. I'd hate to guess what a brand new set might cost now days. Of course they aren't as portable as ebooks.
