Owin via Amazon offers the Owin Women's Vintage Style A-Line Dress in Black or Navy for $25.99. Coupon code "U6R8NAO2" drops it to $20.79. Plus, Prime members bag free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $5.48.) That's $9 off and the lowest total price we could find. It's available at this price in sizes M to XXL.
Note: It's also available in size S for $19.19 after the above coupon with free shipping for Prime members. That's a savings of $11 and also the best deal we could find.