Which HW for a Wifi Bridge, long range (5km) on one side ?

Hi all,

I would like to set up a wifi bridge with a high gain antenna (external, 18 dBi) and sensitive chipset on one side for long range (~ 3 to 5 km) free wifi capture, and a standard domestic antena on the other side to connect to my PC with a domestic wifi dongle (at ~ 30 m).
This "box" would lay outdoor, on top of a high tree .

Do you know a product that can do it please ?
I contacted D-Link and NetGear : they don't have any product for that usage. I have also sent requests to Alvarion and Proxim. But I want a cheap solution of course .

consider the possibility of investigating the How To section at the top of the forum.