ChooseSmart via eBay offers the Guess Men's Sunglasses in Black, model no. GU6800, or Guess Women's Sunglasses in Black, model no. GU7288, for $18.99 with free shipping. That's tied with our mention from a week ago and the lowest total price we could find by $15. They feature 100% UV protection.
Of note, you can buy one of each pair for $32.98 with free shipping.