redlevel has it as far as I can tell. I have a miniscule track on the Model 38 only over the last 10 months:
Smith & Wesson 38 Revolver in .38 Special. 2-in Bbl. Bluebook of Gun Values (30th Edition) indicates between $300 in 95% condition and $450 in 100% condition for this gun. I have 11 recorded prices for this model gun from $300 to $625 over a period of 0 Yrs 10 Mos ending April 14, 2010. The average price as of that date was $432. No refurbs, no refinishes, regular sights all represented as 95% or better, no distinction for import location or engineering revision, if any, no special editions, no distinctions for box, papers, tools. Current or last MSRP is $462.
Here's how the data charts out. There really isn't enough data to establish a trend either in average price or count (availability) but the average looks pretty solid. Pretty much what redlevel posted.