Newegg offers the RavPower 36-watt 4-Port USB Travel / Wall Charger in White, model no. RP-UC07, for $9.49 with free shipping. That's tied with our mention of another color from last month as the lowest total price we've seen. (Aside from the mention below, it's a current low by $7.) It features a total output of six amps.
A close price: Sunvalleytek via Amazon sells this charger in Black for $9.99 with free shipping for Prime members.