Walmart offers the Hanes Men's Boxer Briefs 7-Pack for $19.46. (Amazon charges the same for Prime members; Kmart charges slightly more via in-store pickup.) Choose in-store pickup to dodge the $4.97 shipping fee. That's $5 under list and the lowest price we could find. They're available at this price in size S or L.
Update: The price at Kmart has now dropped to $17.99