King Cobra prices often surpass slightly worn Python prices which IMO is pretty crazy. However, I too rarely see them. One value modifier to consider here is whether the 8in gun is blued. I am not sure that there are blued 8in King Cobras, but I know they are much more rare and valuable when blue.
Many people don't know, but the King Cobra was the last generation of the Trooper. The troopers went from 22 and 38 Troopers, to 357 troopers (replacing the Colt model 357) then to the MKIII variety in 1969, later in late 1970s, the MKV trooper debuted, which was made briefly but discontinued. The successor to the MKV Trooper was the King Cobra.
They didn't sell that well, and also, I've observed many people assume/wonder/ask if they were comparable to a Python, which they are not. They are sort of like a Highway Patrolman in a lot of ways vs a 27. With a lot of people they do of course have the Colt DA allure, when IMO, they would still be made if they were as great as people often claim. I've always liked S&W better in a revolver, but of course, YMMV.