I've bought USB adapters for as little as $10, although you can pay a lot more too. The $10 Tenda ones seem to work every bit as well as the more expensive ones, so I'd go for the less expensive ones. If your computer is a desktop, you could buy a PCI or PCIe card and use that for WiFi as well.
I have an old ASUSTEK Computer with windows xp home edition that has lost its ability to connect to wifi. It no longer shows available wifi connections and instead says a network cable is disconnected. I have spent hours on the internet trying to fix the problem to no avail. I am wondering if I can just buy a new usb network adapter to connect to wifi or do I need to install a new adapter to the computer? Any help would be appreciated.