Meritline offers this USB A to 0.7mm DC Power Adapter Cable for $2.99 with free shipping. That's a buck under the lowest total price we could find for a similar cable elsewhere, outside of the price below. Deal ends today.
If you need more than one, e-part2011 via eBay charges $3.52 plus $1.80 for shipping, when you add two to your cart. That's $0.66 less per-cable than the above mention.
Expect this item to take two to three weeks to arrive.