What you have is a great pump gun in the Win 1300. You don't say what model it is or if it has nice walnut wood or synthetic furniture.
Here is the rub... The 1300 was discontinured in 2006. Since then all the stores have put them on closeout. I have seen the new plain jane models they still have going for as little as $230. There is nothing wrong with the 1300 at all. The big volume stores are just clearing them out of stock. In fact, it has been a while now since I saw the last new one still on the shelf. All this makes the price you are going to receive for your used 1300 lower. I would say a couple of hundred bucks would be the range for you right now unless it is of a special nature. I hate saying that, but it is an honest opinion.
I have two 1300's here. What I want is to find a model with nice walnut wood for a keepsake gun. I have not seen such a model in a long time. One I own is synthetic, and the other is decent wood, but not great.