MakeMeChic offers its MakeMeChic Women's Backless Bodycon Dress in Blue for $19. Coupon code "MMC20" cuts it to $15.20. With free shipping, that's $4 off and the lowest total price we could find. It's available in most sizes from S to L.
Soft Surroundings offers its Soft Surroundings Women's Safari Surplice Dress in Sahara Sand for $19.99 plus $4.95 for shipping. That's $79 off list and the lowest total price we could find. It's available in misses sizes XS to XL and tall size M.