Ann: Southern Cooper Basin Operations Update, page-204

We still don't know how much water there is to be disposed of, and there is a major positive as stated by Bell Potter

"With high levels of natural fracturing, we consider future wells may not require fraccing. This could reduce the well cost by ~0.6m or 17%. However, a portion of this capex saving will likely be diverted to fund the installation of sufficient water handling capacity."

Note the word "portion", so it could still be cheaper to produce than originally projected. But of course at this stage no one knows.