The Windows 7-based laptops will be on clearance prices, and most laptops retail for about twice the manufacture prices.
$300 is fairly limited, although I might just be under Australian prices and you might things a lot cheaper where you are. Your best bet would to look through eBay/Craigslist/any digital seller and do some comparisons.
Just don't go for a Chromebook. They have very poor magnetic resistance and the touchpad will refuse to work depending on what surface you place it on.