I managed to find this one, and it seemed like a likely choice. One that IFI recommends is manufactured by a company called Inside Out networks, and is $90, and is not compatible with Mac OS.
This one, however, works with Windows, Mac OS 8 and 10, and people have gotten it working with a 2.6.x kernel in Linux.
http://www.keyspan.com/products/usb/USA19HS/
I am looking at buying one. When you click the buy now button, it gives you prices ranging from $20-$40, so it is not that expensive.