That'a a toughie! Values of the Colt cobra types depend on finding a person that wants that specific gun for their collection, and is willing to pay you what the Blue Book price says, plus whatever premium you wish to add. Finding that person is not sometimes all that easy.
The best thing to do is put it up on GunBroker at a starting price you can live with if it sells just for that, and no more, or put a higher reserve price on it that you may or may not get, to protect your perceived value of the gun. You may have to relist it a couple of times, and change prices around some to get it sold.
You may get a ballpark value off forum members, but that's about all you can expect on that revolver. My guess would be in the realm of $750.00 plus somewhere?