Oxa via Amazon offers the OXA Ultrasonic 4-Liter Cool Mist Humidifier in Gray for $29.99. Coupon code "5Y9G44FZ" cuts the price to $20.99. With free shipping, that's tied with our mention from three weeks ago, $17 off, and the lowest price we could find. It features up to 16 hours of continuous operation, dial control, and auto shut-off.