I haven't done this myself, but the advice I heard was to go go on eBay and look for a Cuecat. Back in the late 90s some company decided that people wanted to be able to scan barcodes off of print media and get taken to websites. The idea didn't take off, but there were a crapton of the USB scanners made (and, apparently, a PS/2 version as well). Looks like they're running about $10 - $20. I'm not sure what kind of software or modification it takes to use one, though.
There are also barcode scanning apps for various smartphones. If you have an iPhone, Android or Blackberry you might look into that.