Condition is everything.
A 6" Model 19 the target hammer and trigger, box and paperwork in as new or near mint condition will sell for upwards of $1100 to as high as $1500.
In excellent condition, the same target hammer and trigger 6" Model 19 with box and paperwork will sell in $700-$750 range.
Without the box and paperwork, subtract about $100.
Once you start getting into more noticeably worn condition, the prices fall into the $350-$500 range.
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Based on how you describe it, no box, possibly unfired, but with a spot or two of storage wear, it's probably a $600-$650 dollar revolver.
One thing to consider is that pre-internet if a gun shop had something like this and wanted top dollar from the right kind of buyer willing to pay full price, they'd have to wait a long time for them to find the gun. Having a gun sit in the shop a long time cost's the shop money as it's tying up money in guns that are not turning over. The shop was better off making half as much on the gun but selling two or three guns for half the profit in the same period of time. That's where a lot of really good deals came from.
Now however with the internet and sites like Gun Broker, a shop can list a gun like this an attract a much wider market. There's some down side as the buyer will have to pay shipping and transfer fees, but on the other hand the buyer often does not have to pay sales tax, so it's often a wash. However the much wider market reached online means the seller can get a better price in a lot less time and no longer has to wait months or years for a gun with a niche market to sell. That means higher prices.
Which is just background for the statement that there will no doubt be someone coming along to say that the price above are too high - but the reality is that comparable sales prices (as opposed to the listed prices where the gun may not sell) on Gun Broker are hard to argue with when determining actual market value.
The key to understanding gun broker prices is to look at the completed auctions to see what sold, and for how much, as well as what did not sell and the related buy it now prices or bids that did not meet the reserve. Compare those numbers with condition of the firearms and you'll start to see the patterns emerge as to what sells at what price and the differences in condition that result in those differences in selling price.