Right now, ebooks are price fixed. You can EASILY (as in 100% of the time) find new paperbacks for much cheaper at Barnes and Nobel and Borders (as well as Amazon) and cheaper even still at Wal-Mart.
Couple that with the outlay of the reader and ebooks just really don't make much sense from a purely cost perspective.
Now, ereaders are pretty great and they do a lot of cool things. If those reasons compel you to buy an ereader and ebooks, then by all means jump right in. But sticking with paperback books in cheaper in EVERY case. (except for the free ereader books, of course.)