Amazon offers Prime members the uni-ball Vision Stick Micro Point Roller Ball Pen 12-Pack in Black, model no. 60106, for $7.29 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $5.58.) That's 61 cents per pen and the lowest total price we could find for this quantity by $13. These pens feature specially-formulated ink that becomes trapped in paper, helping to prevent criminal check washing and other document alteration.

Note that this item has an estimated shipping delay of three to four weeks.