Newegg offers the refurbished ASUS Selectable Dual-Band 802.11ac / 802.11n Wireless Adapter, model no. USB-AC53, for $19.99. Apply Coupon code "VISACHECKOUT" and pay via Visa Checkout to drop it to $17.99. With free shipping, that's $2 below yesterday's mention and the lowest total price we've seen. (It's also $30 under the best price we could find for a new adapter today.) It features WEP, WPA, and WPA2 encryption. Deal ends October 31.

A 1-year warranty applies, but it's unclear who backs it.