I wouldn't be surprised at $400, in the condition you describe. The adjustable Ruger .32 Mag SAs are getting rare. They're desirable guns and those that have them tend to hold onto them.
It's the "S&W 696 phenomenon" -- a niche gun, not a big seller, but the people who want one tend to be serious revolver buffs who really want one. So owners rarely sell them, and when they do, there's a price premium out of proportion to the demand for the guns when they were still in production.
And the .32 Mag Bisleys can run a lot more than that. If you can find one.
.32 Mag rocks.