AutleyDirect via Amazon offers its Autley AW600 802.11ac Dual-Band Wireless USB Network Adapter for $17.99. Coupon code "2QSE3ZX2" cuts it to $10.89. Plus, Prime members bag free shipping. That's a slight drop from last week's mention and the lowest price we've seen, excluding the below mention. (It's the best deal today by about a buck.) It features a detachable 2dBi long-range antenna and wireless transmission speeds of up to 600Mb/s on 5GHz and 2.4GHz bands.
Don't mind waiting on your deal? Focus-Shopping via eBay offers a similar item for $9.99 with free shipping. Note that it ships from Hong Kong and requires two to four weeks for delivery.