Price is going to depend on location and demand... as you see from the previous replies there's a $100 spread in the estimation.
The 4516-1 is in demand, and I imagine especially so in the states that issue concealed carry permits.
With the original box and paper work, and condition stated, it will have added appeal to S&W collector/accumulators.
My two cents worth is that $500 sounds about right... S&W isn't making them anymore and people that have them tend to hang onto them, like me