That was fast. Hours after Barnes & Noble introduced a Wi-Fi only version of its Nook e-reader and dropped the price of its 3G device to $199 , Amazon responded by dropping the price of its Kindle e-book reader from $259 to $189. Amazon's Web site has been updated, and the cheaper version of the Kindle is for sale now. The Kindle DX is still priced at $489. Amazon said that customers who bought a Kindle that was shipped in the last 30 days are eligible to receive the price difference as a credit. The discounted Kindle e-book can hold up to 1,500 books, includes 3G capabilities, and includes a six-inch E Ink screen. The Kindle is also sold at brick-and-mortar Target stores , though there was no mention of Target in the price-drop announcement. We e-mailed Target to confirm.