SheIn offers its SheIn Women's Floral Print Sleeveless Bodycon Dress in Black for $12.99 with free shipping. (Uncheck "Add Shipping Insurance to your order" during checkout to remove the 99-cent fee.) That's the lowest total price we could find by $8. It's available in sizes XS to L.

Note that new customers can apply coupon code "SHE4" to cut the price further to $11.99.