You will find varying estimates of values depending on what part of the country you are in.
As a general rule nice 10-6's are anywhere from $250-375 depending on condition and the original box and paperwork. There were thousands of them
built and sold to law enforcement and civilians.
The 681 as said before, is the L Frame. Made in lesser numbers than it's adjustable sight brother the 686. Many were purchased by law enforcement
agencies and security firms. I am sure that a number found their way into civilian hands as they usually do.
If you remember that some agencies required officers to provide their own weapon from a approved list, the guns history may not show as sold to a LE agency.
681's are not rare, but not always found in very good to excellent condition either. Very desireable to those who wish a heavy duty service revolver that is capable of digesting Magnum rounds .
A recall from Smith and Wesson on the early 681 no dash, and 681-1's involved replacement of the hammer nose bushing. These will have an "M" stamped in the crane area of the frame by the model number.
In my opinion average value is between $400-$500 in very good to excellent condition and the availability of the original box and paperwork.
I recently purchased this 681-1 from the original owners brother. Less than a full box had been fired through it, but no box or original stocks. I paid $400.