Newegg offers the refurbished Netgear R6200 Dual Band 802.11ac Wireless Gigabit Ethernet Router, model no. R6200-100NAS, for $39.99 with free shipping. That's tied with our mention from two weeks ago as the lowest total price we've seen. (It's a current low for this refurb by $15.) It features USB 2.0, four Gigabit Ethernet ports, an 800MHz processor, 256MB RAM, 64MB flash memory, and concurrent dual band Wi-Fi access for reduced interference.
A 90-day warranty applies, but it's unclear who supports it.