what kind of AR do you want? rails and a crap load of externals? or a basic plane jane "I can shoot at you" AEG? do you plan to upgrade a bnib gun? does it have to be brand spanking new or is used ok?
for a little bit more than $5-600, you could very easily build one through parts in the classifieds and online site supporting vendors.
I wish I had gone the way of building from scratch. it might seem to be a huge task but it's not impossible with a little help. both my mp5 and m4 have very little left of the original guns. everything either was broken, broke, or I just didn't like it so I upgraded it. actually, I think the only original gun part for both of them is the mp5 full stock.
