Average cost is the sum of all prices divided by the number of people that purchased this coral. You are the only person I know who has one. The average cost is what you paid.
I know that doesn't totally answer your question, but I got close!
If it is the same, my electric Miyagi tort seems to be extremely hardy in terms of acropora. My experience is that it's a pretty fast grower and the color combination is nice to see in a tank.