Amazon offers the AmazonBasics 1.0mm Ballpoint Pen 100-Pack in Black/Blue for $3.97 with free shipping when you checkout via Subscribe & Save. That's $3 off list and tied with our May mention as the lowest price we could find. (For further comparison, Staples sells a 60-pack of similar pens for $5.) It includes 50 black pens and 50 blue pens.
Be sure to cancel your subscription once your order ships to avoid being billed for further shipments.