What is a 1975 Ruger 357 mag. SS Security Six 3 barrel worth?

I would buy or sell that firearm for $300.00 to $400.00 dollars. By the way, I've owned my security six for over twenty years and put thousands of high to low loads through it. It's a great firearm to own. I like it better then the GP100's because it's lighter and feels better in your hands.