The 4" was a standard factory length toward the end of the -2 series and carried over into the -3.
As always, prices can vary depending on condition and extras (box, docs, tools). A nickel 4" -2 could likely be more due to number produced as I don't recall seeing one in 4", but that's not to say they don't exist.
I'm not an expert and just my opinion but guessing yours in the $700-$900 range. At least that's where I'd want to be in one like yours at.