And I would say it all depends. I'd ask my uncles questions like this and he'd reply, "How long is a piece of string?" Is the Ruger stainless or blue? What's the barrel length? What's the condition of the finish? Has it had a trigger job? Does it have any extras like a Millett sight, custom grips, etc.? Does it have powder caked around the forcing cone and in the chambers? Does it have any scratches or cosmetic flaws?
I have several brand new Security-Sixes in different barrel lengths, none of which have ever been fired. People keep trying to buy them off me, but I'm not interested as I'd probably buy some just like 'em in the same condition at the prices they'd bring. It's probably the best .357 for the size and money. They're light as Smith's 66s, but much stronger. If someone's going to carry a .357 in the wilderness, they sure won't want a Smith 686 or one of the new Rugers, and the Security-Six is the perfect size and weight. The company was stupid to have stopped making them.
One fellow I knew at the NRA used to walk into a gun shop with six jacketed bullets and drop one bullet into each chamber. He found that if each chamber would catch the bullet that the gun would tend towards much greater accuracy. If a bullet dropped out on the table, however, it would be slightly off. But he was an extreme case. The reason I thought about him was because he loved the Security-Six.
The 6-inch Rugers in stainless are somewhat hard to find, so goin' for $500 in Canada isn't so bad. (I just now found a blue one for $395, so that's only $100 off.)