B&H Photo Video offers the TP-Link AC1200 802.11ac Wireless Range Extender for $49.99. Clip the 60% off coupon on the product page to drop it to $19.99. With free shipping, that's $5 under our July mention and the lowest price we've seen. (It's the best deal now by $10.) Features include speeds of up to 1.2GB/s, a range of up to 10,000 square feet, and two dual-band antennas.
Beware these cash-guzzling missteps when you stop at any gas station.