In reading what Robin G was saying concerning the Blue head versus the Grey head, he questioned which one do you want to bet your skin on. I wouldn't be asking a question about "COST", I would be concerned with "RELIABILITY", TBO, and the heck with cost! Your life could depend on the Reliability of the engine! I would be asking which is more reliable, and which has a higher TBO.
THe higher TBO is a good indicator of which engine is more reliable.