The 27-2 was made from 1962 until 1981. The guns with the "diamond" stocks (pre-1968) will bring a slight premium. The 3.5" barrel is the most popular and will bring a premium. The 5" is next popular. The 6 is most common and the 8" sells for about the same as the 6" barrel. The 4" barrel becomes a standard length in 1979.
What kind of box, cardboard or wooden case? The wooden presentation case adds a premium. Are the papers and tools there? Does it have its original stocks?
From my observation, a ballpark guess for a 6" 27-2 in 95% original finish, in a cardboard box, would be around $350-$375. The same gun with the 3.5" barrel would be $500-$550. A 5" model would be around $450-$500. The late 4" guns usually go for around $400-$450. Add $50 for the wooden case, start deducting for wear beyond the 95% condition. Add for better condition.
If you live in California add 25-50% to all prices due to the laws prohibiting importation of most used guns.
See why it's not as easy as "what's it worth?"