NEW YORK (CNNMoney.com) -- Take that, Kobo. As e-reader competition heats up, Barnes & Noble responded Monday by cutting the price of its flagship Nook to $199 and introducing a low-cost, Wi-Fi-only version for $149.Just hours later, Amazon (AMZN, Fortune 500) hit back. It slashed the price of its popular Kindle to $189 -- a deep discount from the original $259.