I've drastically increased my book spending since getting my eReader. Before that all my books came from the library or library/garage/flea market used book sales ($0.25-0.50 each) or were passed on to me by friends. I've been spending around $50 a month on ebooks, they add up even with an average price this year in the $2-3 range. Of course that doesn't include my two Kindles and the ones I bought my husband and father so they could read my ebooks as well.
As others mentioned, I got the eReader for convenience, not to save money. As a bonus, the quality and suitability of books I'm reading now is a huge improvement over what I could get my hands on cheaply before.