SheIn offers its SheIn Women's Spaghetti Strap Asymmetrical Shift Dress in Navy for $15.49 with free shipping. (Uncheck "Add Shipping Insurance to your order" during checkout to remove the 99-cent fee.) That's $12 off and the lowest total price we could find. It's available in sizes S to XL.
Of note, it's also available in Black or Army Green for $17.99 in sizes XS to L, although not in all color/size combinations.