I know you don't want to spend this much but really something to consider. The $400-$500 MBAir is disposable. The very newest MBAirs use a new Apple designed chip that, from what I've read, is incredible and blows away previous models.
Consider that older Macs run slower on the latest OS and the latest applications run best on the latest OS.
A new MBAir will last 5+ years. An older one may only last one or two.
$1000 buys you speed, security, a warranty and on and on.
Choose your new MacBook Air and select a finish.