TRENDnet 300Mbps Wireless 802.11n Easy-N-Upgrader for $28.99 shipped.  Here is a screenshot for your reference.  Alternatively, it is available at Amazon for $31.24 shipped.  Note that this is not a router itself but is more like an access point.  It gives the advantage of not having to reconfigure the network while adding wireless 802.11n (300Mbps) [...]