The 681 was introduced in 1980
681-1 in 1986, radius stud package and floating hand
681-2 in 1987, changes to the hammer nose and bushing (i.e., the mods involved in the recall, see below)
681-3 in 1988, new yoke retention system
Discontinued in 1992
681-4 and 681-5 were special production 7-shots for Lew Horton and Camfour, respectively.
The no dash and -1 models were part of the recall that included the 581, 586 and 686 to replace the firing pin (hammer nose) and bushing due to some guns locking up when fired with hot loads. Guns that have been modified will have an "M" stamped in the yoke cutout, usually between the serial number and model number.
Value depends a lot on condition and location, probably somewhere around $600 in good condition.