I've had decent success by combining this router:

http://www.pricebat.ca/whr-hp-g300n-buffalo-nfiniti-wireless-n-essential-hig...

with this external antenna:

http://www.pricebat.ca/tl-ant2409a-tp-link-2-4ghz-9dbi-outdoor-antenna/

over a distance of over 200 feet. I don't know if you could do 400 feet without having two of these antennas pointed at each other. (I just used one of these, aimed at the standard omni-directional dipoles of the other router.) This was about the cheapest commercial high-gain antenna I could find this summer. Anything else would likely require time/effort to build your own or more cash to buy pre-made.

The Buffalo Technology router runs the dd-wrt software out of the box, so it's really flexible to set up in various modes. I set it up in wireless client mode, and added a virtual AP, which sets up a separate NAT subnet from the hosting subnet to which it connects. That's all you need for Internet access, but if you need both buildings to be on the same LAN with the same pool of IP addresses, the setup will be a little more complex. Still do-able in dd-wrt, but it may require the same or similar routers on both ends for this setup to work (based on what I read this summer, but I never actually attempted it).

Good luck.

On 01/11/2011 10:25 AM, John Lange wrote:

Anyone have a suggestion for extending Wifi about 400 feet between two buildings on the cheap?

A point-to-point solution of some kind?

John