Sunnyvalleytek via Amazon offers the RavPower 15,000mAh Solar-Powered Dual-USB Portable Battery Pack with Flashlight for $32.99. Coupon code "solarpb3" cuts that to $27.99. With free shipping, that's $72 off list and the lowest price we could find. It features an IPX4 waterproof rating, two USB ports, and LED flashlight. It can also be charged via a DC5V/2A input.

Update: Redeem the coupon on the product page under "Pay $25.99 for 1st RAVPo..." to drop the price to $25.99.