looks like GB completed auctions lists the sold prices in the ranges already mentioned. One exception is this nice example that sold for $350.
Smith & Wesson Model 640 (no dash) .38 Special Penny Start/NR - Revolvers at GunBroker.com : 878575700
Damn, wish I had seen that up for auction. But i wasn't looking for one because I have one that I don't carry any more...the 642-1 has taken over.