Proozy offers the Reebok Men's Stretch Boxer Briefs 3-Pack in several colors (Black/Magnet/Black pictured) for $19.99. Coupon code "DN1375" cuts the price to $13.75. With free shipping, that's $1 under our January mention and the lowest price we could find by $5. They're available in sizes S to XL.
With these companies, it might be easier than you think to negotiate your monthly bill down.