I've been keeping track of the books I've read this year, along with the price I've paid. Most of my purchases are at fictionwise.com and webscription.net.
So far this year, I've read 52 books at an average cost of $2.99
These are mostly modern SF/Fantasy, with an occasional classic, although only three have been free (promotional or out of copyright) books.
My most expensive book so far this year was
The Girl Who Married a Lion by Alexander McCall Smith at $7.61. Oddly, also one of my lowest rated (although I loved his No.1 Ladies' Detective Agency books). Two were just $0.95 - my lowest non-free price this year:
Inferno by Larry Niven and Jerry Pournelle and
Lord Edgware Dies by Agatha Christie.
I fear that with publishers starting to control retail prices directly ("agency model"), my average ebook price will rise once I start buying again. But since I have over 400 ebooks in my TBR folder, I don't anticipate buying many more ebooks in the near future!