You are thinking in hard way.
Forget about the USD price, you dont need it.
Simply consider that:
Cost of hardware + cost of electricity*time / BTC production
Considering:
- 150 EH/s of hashrate growing at 145 PH/s per day.
- 144 blocks per day.
- fee reward is not included.
- 6.25 BTC block subsidy.
- 100 TH/s, one miner.
- 3250 W power consuption.
- 8000 USD cost of hardware.
This give you a graph like this:
https://imgur.com/tsA90ya*Where Y axis is Price in USD and X axis is days passed since start of mining
When this curve will be UP related to Bitcoin price, then mining will be profitable. You can take a better pic seeing this table
https://imgur.com/LSBI7T1*Where x is days, X is USD price and B is the amount of BTC obtained at given X value.
As you could see, mining allow you to obtain BTC at a price below to 50k for almost 10 years.
