For in-store pickup only, Micro Center offers the Inland 2,600mAh Portable Battery Pack in several colors (Black pictured) for 99 cents. Outside of the price below, that's the lowest price we could find by $5 and the cheapest power bank we've seen. Update: It has since sold out.

Don't need it soon? Rainway87 via eBay offers it for about 83 cents with free shipping. It ships from China and may take two to three weeks to arrive.