Meh.
The -3 changes were the elimination of the counterbored cylinder and pinned barrel. The very late -3(stamped -3E) guns received Endurance Package upgrades, as did the later engineering changes(higher numbers after the dash).
-3 guns are the red headed stepchild of the M29s. They weren't made like the "old guns" and didn't have the improvements of the new guns, and as such, they generally bring less money than either earlier or later model guns. The price you quoted seems to be about average for them. I could have picked one up not long ago for under $400, but passed because it was a well used gun--still looked gun, but had been shot extensively and was loose.