Amazon offers the TP-Link 802.11n Wireless N Nano USB Adapter, model no. TL-WN725N, for $9.99. Clip the the $2 off coupon (located below the product price) to cut it to $7.99. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $8.13.) That's the lowest total price we could find by a buck. It supports WEP, WPA, and WPA2 security and speeds up to 150Mbps.