SheIn offers its SheIn Women's Sleeveless Backless Pleated Dress in Navy for $17. Coupon code "NEWSLETTER3" cuts it to $13.99. With free shipping, that's $12 off list and the lowest total price we could find. It's available in sizes XS to L.
Note: Uncheck "Add Shipping Insurance to your order" during checkout to remove the 99 cent fee. It ships from mainland China and should arrive in three to four weeks.