USB wifi adapter

I am trying to make a raspberry pi into a wireless access point but i want it to cover a very large area much larger than the average house, would there be a way to do this with a usb adapter or should i just connect it to a wireless router of some sort?

For that size area anything running off usb wont have enough power to do so.

Access points are so cheap these days with a bucket load to choose from. http://www.pccasegear.com/index.php?main_page=index&cPath=200_634&zenid=a2e65f3a058c7c73da09e0e5c2817b54

If I were to do that is there any way to set up a second access point to extend the rang of the first without having to use a cable, such as something in dd-wrt?