My dad is a retired NYSP (New York State Police) Officer. He put 23 years in on the job. I gave him a call and asked him about the Model 65. The Model 65 was one of the departments assigned handguns, replacing the Model 28 in 1981, before adopting the Glock 17 in 1990. 3" (round butt) Model 65's were carried by detectives (B.C.I. - Bureau of Criminal Investigation) and 4" Model 681's (square butt) went to uniformed officers. The Model 65 is essential a stainless steel version of the Model 13. S&W discontinued the Model 65 in 2004. I don't think the "NYSP" stamp adds or detracts anything from the value. The NYSP are now in the process of replacing the Glock 17 with the Model 37 (45 GAP).
100% value would be around $400, 95% $300, 90% $250.
Other previous NYSP handguns include the Colt Model 1917, Colt Official Police, and S&W Model 13.