Amazon offers the Switronix GoPro 3/3+ Battery Eliminator USB with 10-Foot Power Cable
, model no. DVGP3USB, for $18.50. Clip the $5 off
coupon to cut the price to $13.50
. Plus, Prime members bag free shipping
. (Non-members can spend $35 or more to bag free shipping; otherwise, shipping adds $5.10.) That's the lowest total price we could find by $3. It allows you to power a GoPro from a USB power source and works with Skeleton Back Door.
: Note that this item usually ships within 2 to 3 weeks.