Aropey via Amazon offers its Aropey Aromatherapy Cool Mist Essential Oil Diffuser for $19.99. Coupon code "MYWDLK50" drops it to $9.99. With free shipping for Prime members, that's the lowest price we could find by $13, although we saw it for a buck less last week (since expired). It features a 120ml water tank, LED lights, and automatic shut-off. Deal ends October 21.