I have a track on the 4-inch, non Jerry Miculek version which replaced it. It's a very popular revolver and, except for the JMs, doesn't show up used very often. The 5-inchers are a little more common but either size will demand significant bux as far as I can tell.
Smith & Wesson 625 4-in Bbl Revolver in .45 ACP. Bluebook of Gun Values (33nd Edition) indicates between $452.5 in 95% condition and $685.25 in 100% condition for this gun. I have 51 recorded prices for this model gun from $400 to $950 over a period of 8 Yrs 11 Mos ending July 10, 2012. The average price as of that date was $572. 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 $979.
Here's how the data charts out. You can see the price tended to about $660 as of June this year. There was a flare of the 4-inchers showed up back in 2003 when there was a rule change in a popular competition. The 4-inchers were winning too often and were replaced by the 5-inch version. After that, the 4-inchers have been few and far between and they seem to appreciate in value faster than inflation devalues bux.
I have one. It doen't have all the bells & whistles, or grips, of the JM version but it sure is accurate, mild, and a pleasure to shoot. Find one, buy it.