This is irrelevant, how many BTC in existence makes no difference in calculating the cost of mining 1 BTC in 2020 


So is this.


And this.

And the rest is dynamic inputs unless he has a crystal ball that tells him the price of bitcoin in the future as well as the difficulty of every future epoch, this is nothing but pure speculations that can be far from accurate.


This can be wrong with the same probability of being right.

I am not trying to underestimate the efforts but this does not make a lot of sense, the result you seeking is based on factors that are unseen, unknown and pretty hard to predict.