Tanga offers the refurbished 2.4-lb. Apple MacBook Air Intel Haswell Core i5 1.4GHz 11.6" Laptop, model no. MD711LL/B, for $475.99 with free shipping. That's $104 under the lowest price we could find for a refurbished unit. It features an Intel Haswell Core i5-4260U 1.4GHz dual-core processor, 11.6" 1366x768 LCD, 4GB RAM, 128GB SSD, 802.11ac wireless, Bluetooth 4.0, Thunderbolt, and Mac OS X 10.11 El Capitan.
Note that a 90-day warranty applies although it's unclear who backs it.