ColtCollector, welcome to Coltforum!
I was unaware that any Colt Cobras were ever made with 6" barrels.
Also, no Colt Cobras were manufactured from stainless steel. Some were nickel plated. You must be discussing one with nickel plating.
Colt Cobras have shot up in value in the past several years.
I cannot opine on the value of an object which I think was never produced.