http://www.islandtimepc.com/marine_wifi.html

Very sensitive, longer range than anything I've seen, and it runs on 12 volts. You basically just mount the antenns, plug it into the network port of the computer and you're on the air.

You can Google around and collect the individual parts of this and save perhaps $40, or just have this guy send you one.

There are cheaper aternatives but they aren't nearly as good. This thing really works well.