Your 28-2 likely shipped somewhere in early 1980. Value greatly depends on condition, location and completeness...(box, papers, tools). A nice complete 4" 28-2 in my area could go for $750-$800+ depending how much someone wanted it. It's only worth what someone's willing to shell out for it. BTW, welcome to this fine forum!
Welcome to the FORUM! Get on Gun Broker and search S&W Model 28. There will be a list of them, and what is being asked for them. The key is to LOOK at what they actually sold for. JUST a TOOL! Bob