off the shelf new from a LGS, you're looking 800-1K. used would be a bit less.
or you could build one and save some $$. (depending on what you really want.)
If you just want an average run of the mill AR, and don't want to "build" it yourself, my suggestion would be to order a built lower and then order a complete upper. ordering them sepaerate exemts you from the federal exercise tax. i think the tax is something like 200 per rifle.
hope this helps.
SM