Yup -- I've noticed the pricing difference. Every mailing I get for ereader books (from my long years reading on the pda, I'm still on the mailing list) -- I check the price on Amazon before buying anything, and it's always been better on Amazon. So far, anyway. Guess that was part of why I picked the Kindle -- but you probably got your Sony earlier and before Amazon got into the game.
Maybe somebody wants to buy your Sony, and you can switch...... the Kindle is really better in person than it looks to be in pictures.