ShoeBuy cuts 20% off sitewide via coupon code "20FEBRUARY". Plus, it evens stacks with many items in the sale section. Even better, all orders bag free shipping. Some brand exclusions apply. A couple best bets with prices after coupon:
ShoeBuy offers these 2 Pairs of Darn Tough Men's Vermont Micro Crew Socks in four colors (Oatmeal pictured) for $37.95. Coupon code "WINTER2015" cuts it to $30.36. With free shipping, that's the lowest total price we could find by $10. They're available in sizes S to XL, although not in all size/color combinations.