As a potential buyer, I'm not sure how much stock I put in the number of rounds that have been fired in a gun. There is simply no way to verify that information. For a private, face-to-face sale of the gun (providing it is in really good shape), I would guess you might get anywhere from $550 to $650 for it. Of course you will get many low-ball offers, but eventually someone will give a fair price for the gun. If your LGS is like the ones that I deal with, they will give you no more than 50% of what they will retail it for. So what that means is if they put a $699 price tag on it, you would hopefully get $350 on a trade-in.
I have been guilty of trading in a gun for much less than I could have sold it for in a face-to-face transaction because I REALLY wanted a gun that I saw under the counter. I always knew that I was getting screwed on the deal. Hopefully, I have become more patient in my gun dealings at this point. If I miss a buy, there is usually another one that I can find AFTER I sold my old gun in a private transaction. I live in Texas, so it is very easy for us to sell guns face-to-face. Good luck!