I have some bad news for you (and anyone can feel free to correct me if I'm wrong), but I don't think anyone makes PCI sound cards compatible with Macs + OS X other than M-Audio, who makes the Revolution 5.1 & 7.1 cards, which are NOT $20 or less. Otherwise, the only other options are external Firewire and/or USB audio devices, which those too tend to be over $20.