It helps if we know what the asking price is. If nothing else, "inquiring minds want to know".
$500 would probably make it a good buy. A gun show dealer in my area used to have a LNIB 4" M28-2 priced at $650. He doesn't have it any more so I assume he got his price. (The dude is ... uh ... "difficult" so I don't talk to him much. Thus this is all I know about it.)