The 16-4 is a very desirable gun. Its what those of us who can't afford an earlier Model 16/K-32 end up settling for. They're also outstanding shooters and not a whole lot of them were made. I consider the 6" to be the most desirable.
$1000 would be the low end. $1200-1300 would be reasonable, but to the right buyer, $1500 isn't out of the question. It just depends on how bad you want it.