Just found this on eBay:

http://www.ebay.com/itm/Netgear-WNCE2001-Universal-WiFi-Wireless-N-Extender-Ethernet-Network-Adapter-/270921577406

$30 with no tax and free shipping. About as cheap as they get. I just grabbed one, though I really shouldn't have. I'll have to skip a few lunches to pay for this one.