I've had my Kindle 3 since early September but have so far read only 6 books on it (I'm on my 7th one now). They were all freebies! So: $0.
I've
acquired quite a few ebooks since I got my Kindle, including non-free ones; however, I've still only spent $0.36 because I bought them all using gift cards I earned at various websites.

Yay!