Rock River makes good stuff but please don't spend your hard earned on a very nice rifle like a RR and then go crappy on the scope. There are decent scopes out there for under $500 if you look around, i.e. the Bushmaster Elite 3200 or 4200 line are mostly under $500 and aren't bad and the Falcon line of scopes are good for the money as well. I've used the Konus M30 and the Leupold Mark AR scopes and they are mostly under $300.
I hope this helps a bit.