Ebay offers Anker 10000mAh 12W Power Bank for $12.99 (reg $29.99) with free shipping.

Product Description:
With a substantial 10000mAh capacity, the 323 Power Bank can charge most phones over 3 times, ensuring you're always powered up. This power bank offers dual charging capability, allowing you to charge up to 2 devices simultaneously through its versatile 2-way output. Stay in control with the precision digital display that showcases the exact power percentage, making monitoring intuitive. What's more, its Bluetooth-friendly design features a specialized small current mode, making it perfect for efficient charging of Bluetooth devices.

• Dimensions (Overall): .65 Inches (H) x 3.26 Inches (W) x 6.55 Inches (D)
• Weight: .59 Pounds
• Batteries Charged Simultaneously: 1 (max)
• Volts: 5 Volts
• Battery Capacity: 10000 (mAh)
• Package Quantity: 1
• Wattage Output: 12 Watts
• Rechargeable: Rechargeable
• Battery: 1 Non-Universal Lithium Ion, Required, Included