strikethree

You need to think of it like the NPV of any project in that you are just discounting future cash flows less the cost of starting the project in the first place. I think Paraguay meant to say you subtract initial costs not sunk costs. You don't subtract sunk costs because by definition they are costs already incurred so do not need any consideration in the value of the project going forward. The miners sell at the future spot price which from a budgeting point of view is best given by the futures price which as deriv108 correctly points out takes into account of the lease rate.