Instead of using 1% or 5% (which seems to be very arbitrary, 5% is 5 times more than 1%, and reflects one person's opinion) - why don't you look at the report that was produced last year detailing a NPV for the Eagles nest?

They provided sensitivities for things like concentration and resource price, and outlined their assumptions on infrastructure (see the line graphs). A few adjustments and you can easily get a ballpark number for NPV of the project given the additional information that we now have.

Once you have the NPV, you know what the project (EN) is worth, and you can begin to approximate how much a take-out would go for. Note, they also gave sens to differnt discount rates, so you could even use those to approximate the the take out price using a higher discount rate (to reflect the riskiness of the project).