Some rough maths on the value of this potential off-take

Thought I'd post the quick and rough/estimated maths I've done today on this deal for others to see (or correct).
Prices are in USD. AUD conversion will be at the end.

2.5m tonnes * $126 = $315m
$50/t operating costs = $125m
Profit = $190m
Debt/Royalties = $50m

Total $ remaining after everything = $140m

Mined @50,000t/m we can expect the 2.5m tonnes to be mined in a little over 4 years. I'll allow 4.5 years to ramp up.
$140m / 4.5 = $31.1m per year profit

The AUD conversion: $185m profit / $41.1m per year

I would expect our MC to be worth around that $180m if this deal goes through and all my estimations are correct. That's ~500% from here.

I'll add that it's true that we don't know the price we will sell at. $126 was mentioned and it was also mentioned that there would be a discount to that. Though my understanding is that we have a higher than average quality coal so we may see around that $126 figure. I also think I'm being conservative with my operating cost of $50/t. I've heard $40/t been thrown around this space a few times so you can add $25m USD/ $33m AUD to our profit if that's the case.
My MC estimation also does not include anything to do with BBM or TBAR.

Thoughts? Anyone want to correct me?
I'm encouraging discussion here