Oak Leaf via Amazon offers its Oak Leaf 3.4-oz. LED Ultrasonic Essential Oil Diffuser for $19.99. Coupon code "Q8WMVZ3K" drops it to $11.99. Plus, Prime members receive free shipping. That's the lowest price we could find by $13. It features two misting levels, a 7-color LED light, and automatic shutoff. Deal ends May 31.