I follow a rule of thumb that was first mentioned here about a year or two back: any mechanically sound N-frame with a halfway decent finish on it (which basically means not pitted, rusted or abused) is at least a $400 gun. Then you start adding dollars for model scarcity, better condition, value-added features, general desirability in your own eyes, and so forth.
I would look hard at a 60-year old nickel gun in top condition, because there is always the chance it has been refinished. That's a value-killer as far as collectors are concerned, but may mean nothing to someone who just wants a utilitarian large-frame .38 for general purposes. If it has had its chambers lengthened to take .357 Magnum rounds, that kills not just collector value, but collector interest as well. A dead givewaway for a careless refinish would be plated hammer and trigger. They should ALWAYS be case-colored. If they remain CC, that's good -- but look for other refinish hints like an overpolished gully where frame and sideplate come together or light/missing rollmarks.
Can you share the serial number, or at least tell us whether it had an S prefix? With the S, it is either a postwar transitional HD or a Pre-Model 20. (I'm assuming you would have told us it was a Model 20 if it was model marked.) A nickel transitional with a good original finish is easily worth $600 (and possibly a lot more), and a Pre-20 may be worth that much. If it is a somewhat uncommon prewar four-inch gun with original nickel finish, so much the better.
Sorry about the conditional answer, but at this stage there just isn't enough detail to give you a simpler one. Pics would really help.
