The value/price gap is quite wide and depends upon mechanical and finish condition and its originality. You would need to describe the condition much more thoroughly and then try to determine if the nickel is original or refinished, and the grips as well. Also, if the gun has been altered in any way.
A good place to get price comparisons is to go to the Old Town Station auction site and see what Nahas and Supica have sold these for in similar condition over the last few auctions. They will have nicely described and photographed examples and the prices realized. For a gun w/o any particular historical connection (like a Wells Fargo or other connection), $2000 would be fair for a "good" or better condition gun in original (unrefinished, with original stocks) condition.
You also need to know what you are looking at; there are dizzying variations on the "#3." Based on date and caliber, sounds like you have a First Model Russian - but the letter should make all that clear. I would also carefully measure the barrel correctly and compare it to the letter - 6.5" was not a standard production length, and examine it for evidence of alteration (this significantly alters value downward). The letter should also state what stocks it shipped with, wood or ivory. Sometimes this is not known, but usually it is.
I you post a few detailed photos of the gun and the wording of the letter (usually only the last paragraph or two address the gun in particular, the rest is general history of the model), you can get much, much better advice.
I am not an experienced collector of these, but I have been studying them in detail for about two years trying to find the one I want to buy. The one you are talking about could well be a great buy, but doing some homework and verifying everything is wise. You may also want to consider finding an antique gun dealer or expert near you (or within a couple of hours at any rate) and have him give you an opinion before buying - at $2k, $50 or $75 for an hour of appraisal time could be well worth it. The Jinks letter will tell you how it left the factory and where it went 125 years ago, but it takes an experienced eye to tell you what you have in front of you now.