Check these folks out:
Data Alliance: Long-Distance Wireless Networking Equipment & Support
I bought a WIFI card, omni antenna (marine, no less!), appropriate cables & cords, for just a little over a $100. In the marina, I could barely get the WIFI from the shoreside bathroom 200' away. Now I get over 70! Of course, most are barely there, but it is amazing. The WIFI is 100X faster than my ATT air card. A buddy is cruising in Mexico with the same setup, & we can skype while he is at anchor...
I have no financial interst in Data Alliance. Their tech info was helpful when I had trouble getting the driver to download from the supplied CD.
Mike