I did some web searching, and although I may have missed some, most of the 36" x 36" machines I saw started around $7000.
The only one I know of is the K2CNC. It's only 25" x 39", though. I recommend reading this thread before buying one, especially the messages at the end. http://www.cnczone.com/forums/showthread.php?t=8660
Here's the link to the machine. http://www.k2cnc.com/KG-3925_detail.asp
$3100 with no motors or drives.