With orders of $25 or more, Amazon offers Prime members the Pilot Precise V5 Roller Ball Pen 7-Pack in Assorted Colors for $2.05 with free shipping. That's $0.29 per pen and the lowest price we could find by $8. Each pen features a 0.5mm tip.

Note: This item is offered as part of Amazon's "add-on program" and can only be purchased with an order of $25 or more.