Electronica Direct via Amazon offers Amazon Prime members the refurbished Linksys AE1000 802.11n Wireless-N USB 2.0 Network Adapter for $13.99 with free shipping. (Non-members can spend $25 or more to get free shipping; otherwise it adds $5.58.) That's the lowest total price we could find by $4, although we saw it for a buck less three weeks ago (since expired). It features WPA and WPA2 encryption.

Note that no warranty information is provided.

Amazon Prime membership is $79 per year; however, Prime is free for college students for six months, and free for parents and caregivers for three months.