Fry's Electronics offers the PNY 2,600mAH Portable Backup Battery for Smartphones
, model no. P-B-2600-1-S01-RB, for $14.99
with free shipping
. That's the lowest total price we could find by $9. Features include a digital power indicator and 20" microUSB cable.
Note that it's currently backordered, but it can be ordered at this price and will ship when available.