One problem with trying to extend WiFi range is assembling all the necessary gear to establish a strong directional signal both ways. HD Communications' HD262000 aims to be a simple, all-in-one point-to-point WiFi bridge kit adding up to 5 miles of range to 802.11b/g networks.
The HD26200 is made up of two high performance Ubiquiti network radios with integrated 17dbi dual polarity antennas that are configured in wireless bridge mode. The HD26200 bridge is also powered over ethernet, so no RF cables are required, only an outdoor CAT5 cable to bring both data and power to the radios.
At $318, it's not too expensive, especially given that it runs on PoE and doesn't require one to fiddle around dismantling routers to hook up tiny coax connectors. Unfortunately, it also requires direct line of sight: here's hoping that this is just to get the full advertised range. My own adventures in wireless bridging failed, even over a far smaller distance, thanks to thick brick walls between my router and my target machine.