New $300 laptop computers are available for purchase on the market but they come with 7 inch screens and a hard drive capacity of just 2 GB. If you want a new full-sized laptop computer with at least an 80 GB hard drive then you're going to have to increase your budget to at least $399. Ebay and some other computer auctions are the only places I can think of where you could buy $300 laptops. Keep in mind that $300 laptop models sold on auction sites are probably going to be used with the actual condition dependent upon the seller and whether any recertification or refurbishment takes place prior to shipment.
In case you didn't know, there are new desktop computers on the market that start at $199 and are suitable for surfing the internet safely, receiving and sending email, listening to and burning CDs, watching DVDs, and downloading or saving a reasonable amount of files. The cheapest laptops typically go for $399 although Asus does produce the 7 inch miniature model that starts at $300(remember it only has a 2