Aropey via Amazon offers its Aropey Aromatherapy Cool Mist Essential Oil Diffuser for $19.99. Coupon code "RNCLKS5J" drops it to $9. With free shipping for Prime members, that's tied with our expired mention from three days ago and the lowest price we've seen. (It's the best deal now by $14.) It features a 120ml water tank, LED lights, and automatic shut-off. Deal ends October 16.