I believe you have your models mixed up and one reason you are having a tough time getting a ball park figure.
First off it is not a model 66 if it has a blued finish. The model 66 is stainless steel. The "6" prefix in S&W handguns is for stainless steel guns.
If in fact it is a "highway Patrolman", it is a model 28 that came in blue finish and both 4" & 6" barrels. They quit making that model in the late 80's.
Try searching under model 28 S&W and you should find a ball park figure. Too bad it was not the model#27, which was the dressed up version of that gun and worth about $ 100.00 more then the #28 Also I believe the model 28 was on the "N" frame and not "K" frame. If it is a "K" frame gun, you may have a model 19. If it does have stameped on the barrel, "Highway Patrolman" it is a model #28 N frame 357 mag.
RELH