I sold an older stainless 3"er a couple of weeks ago for $325. Probably could have gotten more, but it was a quick, painless sale to a guy at work. Bought a real nice 4" GP to replace it for $325, and all I was really after was an even trade. I'd say the $400 mark would be a good place to start.
I assume .357, if .38 then it is VERY special.
This is an out of production model. Current value is still in the $400 + or - range but I would guess it will be going up. Now if it was the short lug version, it woud be quite rare.
Stainless is easier to care for but the blued is not as flashy in the dark. Some folks just prefer blued.
The short lug is more noticable on the 4" and 6". I got sort of focused on the fixed sight versions. I'd like to pick up some of the .38s but the import restrictions in Ca. make it more difficult. I think any .38 GP will be considered rare in the future.