Ninja Sox offers its Ninja Sox Unisex 3.0 Socks 6-Pack in Black, Charcoal Grey, Heather Grey, Neon Green, or White for $32.99. (Choose "6 pairs" from the drop-down menu to see this price.) Apply coupon code "Ninjasoxhalfdozen" to cut that to $19.79. With $3.99 for shipping, that's $13 off list and the lowest total price we could find. They come in sizes S to L.
Of note, you can buy six pairs in mixed colors and sizes for the slightly higher price of $21.56 with $3.99 for shipping by adding six individual pairs to your cart and applying the above coupon.