Ending today, Vitamin World offers two Vitamin World Chilled Shaker Cups (pictured) for $6.99. (Search "029049" to find them. Add two to cart to see this price.) Better yet, coupon code "VWFLASH" cuts that to $5.59. With free shipping, that's $8 off and the lowest total price we could find.
Vitamin World also offers two Precision Engineered 20-oz. Shaker Cups for $6.99 before the above coupon, $5.59 after. With free shipping, that's the lowest total price we could find by $7.