Tonerone via Amazon offers Prime members the Tonerone 13.5-oz. Ultrasonic Aromatherapy Essential Oil Diffuser and Cool Mist Humidifier in Black or Yellow for $19.99. Coupon code "EXHD9DGR" drops it to $15.99. With free shipping, that's a buck under last month's mention and the lowest price we could find today by $12. It features a 13.5 oz. capacity, two mist modes, seven LED light colors (with steady and rotating modes), four timer settings, and auto shutoff.