Well Fiasco, to tell ya da trute, that's not a Nickel plated gun. To the best of my limited knowledge, Colt never produced a King Cobra , Custom Cobra or even a Combat Cobra in nickel. Those were all offered in Bright Polished Stainless.
Now then, back to your question of value. The Combat Cobra's & Custom Cobra's were done in a very limited number. Any of those will bring about a grand and up for a minty example. As for the standard issued Bright Finished King Cobra's, those have actually been bringing fairly nice premiums, compared to the standard satin finish that was offered. The Bright ones are bringing anywhere from $600 and up for minty examples. The hardest to find standard production King Cobra's would be any with a 2.5 inch tube. Those little barreled suckers are pretty darn hard to find. there's a lot of collectors that have not even seen any in person.
Hope that helps a little.
And yall wondered why I never fired mine (talk about making a profit). Here is another little tidbit to file away. Mine came near the end of the run (CC09xx) and came in the blue plastic box not the cardboard box.