Amazon doesn't publicize it, particularly at this time of year when they may drop prices on many items, but if they lower the price on something you bought in the last 30 days you can contact them and get refunded the difference.
I myself learned of the 30-day price guarantee from my friend (and occasional Slate contributor) Joshua Green, who bought himself a plasma TV screen a few weeks before Christmas. Checking the price a few days after Christmas he found that it had gone down $20, so he dialed Amazon customer service, asked for his refund, and got it. After hearing this story, I phoned Amazon (don't forget, now: 1-800-201-7575, extension 7) and, like a tippler seeking entry to a speakeasy, uttered the secret pass phrase: "Does Amazon offer a 30-day price guarantee?" There was a pause at the other end of the line. Then, as if opening the door to a stranger, the customer-service rep said warily: "Yes, we do."
Happy New Year to you, too.