Let's try this...
if it's pinned & recessed (P&R) (which most (all?) 19-4's are) and a 4" barrel with original grips, it may fetch as high as $450 when bought from a dealer, for some reason the 6" barrels are LESS desirable and may fetch about $400. Take at least $50 off this for a private sale and at least $85-$100 off for a trade at a dealer. The other size barrels, mostly 2 1/2", are probably at least as valuable as a 4" barrel and the 2 1/2" probably came with a round butt which many like for ccw. "Shooter" condition P&R K-frame blue Smiths probably bring at least $50 more than a non-P&R in similar condition.
This is probably a ball park figure for "fly over country" and will probably be higher on either coast. HTH