Newegg offers the Asus Dual-Band 802.11ac Wireless USB 3.0 Adapter, model no. USB-AC55, for $19.99 via the directions below. With free shipping, that's tied with our mention from last month as the lowest total price we've seen. (It's also a current price low by $10.) It features WEP, WPA, and WPA2 encryption. Rebate expires September 30. To get this deal:

1. View the Asus Dual-Band 802.11ac Wireless USB 3.0 Adapter for $49.99
2. apply coupon code "EMCAXKR29" to cut it to $39.99
3. redeem this $20 mail-in rebate for a final price of $19.99