I've been looking for my first AR recently. I really want a Colt. Money is a serious factor at the moment (already bought a Garand and reloading equipment/supplies this year!). I looked around myself, searched, and posted in the official "where to find" thread stickied here. The best deals seem to be: The occasional LGS, some Walmarts, and (for currently in stock) the two below websites.
If I were to consider a used 6920 I wouldn't personally want to spend more than $800-$850. $100-200 for a brand new gun I KNOW hasn't been fubar'd with is a premium I would be willing to pay. I can only assume plenty of other people think the same way. But that assumes that they know where to get the properly priced new guns.
G&R Tactical
http://www.gandrtactical.com/cgi-bin...ction&key=6920
DSG Arms
http://dsgarms.com/ProductInfo/CO6920.aspx