I have the Ruger Blackhawk 357 and a 6 inch barrel. This is a very nice and reliable revolver. I think it should be worth 550. These are classic handguns. I am not so sure about the semi autos made by Ruger. I have found my Black Hawk to be very reliable.
I know the Rugers are reliable. My dad bought a new Super Redhawk .357 mag stainless in the mid-70's to carry on the Franklin Police Dept. He still has that gun, and he guesses over 200,000 rounds have been put thru it. All he had to replace was a spring or two. It still shoots well, but he has sort-of retired it to the glass display case. I'm sure his wouldn't fetch a lot of money, but it still looks nice and dad would never sell it anyway.