Walmart offers the Better Homes & Gardens Cool Mist Ultrasonic Essential Oil Diffuser 7-Piece Set in Off White for $12. (Other colors are also available for a few bucks more.) Choose in-store pickup to dodge the $5.99 shipping fee. That's $28 off and tied with our mention from last week for the lowest price we could. The 50mL diffuser comes with six 5mL bottles of essential oil.