When I first got my Sony 505 I thought ebooks would be cheaper than pbooks. The ones I was interested in weren't. So I decided to change my reading habits. I never buy an ebook of a New York Times bestseller. Rarely worth the price or the time to read.
Instead, I "buy" most of my books at
Smashwords. I've discovered a lot of well-written indie author ebooks at $2.99 and less, most often free, at Smashwords. I think if you are only interested in newly released bestsellers, an ereader is a mistake. If you are willing to try writing from unkown authors, then the device is great because there is a lot of free and inexpensive writing available that is very good.