Newegg offers the refurbished ASUS Black Diamond Dual-Band 802.11n Wireless N600 SOHO Router, model no. RT-N53, for $14.99 with free shipping. That's $24 under the lowest total price we could find for a new one. This is a concurrent dual-band router, meaning it can run two separate full-speed 802.11n wireless networks at the same time.
A 90-day warranty applies, but it is unclear who backs it.