Sunsmile*2013 via eBay offers this Women's Tank Dress in Rose Red or Blue for $5.99 with free shipping. That's the lowest total price we could find by about a buck. It's available in one size fits most.
Note that this item will arrive in three to eight weeks.
Ralph Lauren offers its Polo Ralph Lauren Women's Mesh Polo Minidress in Blue Albatross (pictured) or Evening Post Red for $44.50 plus $5 for shipping (select "Economy" shipping at checkout). That's the lowest total price we could find by $20. It's available in sizes XS to XL, although not in all size/color combinations. Deal ends September 1.
Venus offers its Venus Women's Ruffle Bandeau Dress in four colors (Sapphire Blue pictured) for $26. Coupon code "XWEB1589012" grabs $4.95 for shipping. That's a savings of $13 and the lowest total price we could find. It's available in sizes S to XL.