What it's worth really depends on how bad you want to sell it and how bad somebody wants to buy it. Before '08 you could buy them around where I live for $600ish. Bud's has them now for $671.
DPMS RFA2L16 PTHR LT16 223 FXD $671.00 SHIPS FREE
If I really wanted it, I'd give you $500 if it was in good shape. But, like I said it really depends on how bad the buyer wants it...and how bad you want to sell it. If you shopped it around and found the right buyer, you may be able to get $600, or you could probably "quick sell" it for $400.
As always, ymmv.