I'm a member of the Austin Wireless Group, a group that helped business owners setup wireless hot spots all across Austin. Here are some notes that I've gleaned from our e-mails.

Murray Freeman of Wi-Fi Texas suggests:

Use two TR-6015's from Tranzeo - complete with built in antenna and outdoor packaging (about $240 for each end). Cross link them with WDS. Mount them on the outside of the building. All done!

For a cheaper route (that will work "mostly"), you can do the same thing with a pair of Buffalo Tech WHR-HP-G54s (about $60 each) coupled with a pair of Hawking Tech directional antenna to put outside (about $60). Make sure your antenna has the RPSMA adapter with it.

There are many products between these price points....