Thanks, that was a really quick check. And yeah, that would increase the costs markedly.
(My initial thought on posting was that $30 billion would not be enough, though the first read of actual per-mile costs, neglecting per MW-mile, seemed to suggest otherwise.)
This PDF from Wisconsin puts the cost at $280k-390k/mi depending on the voltage of the line. They put the cost of underground transmission lines at $1.5M-2M/mi for the same voltages.
(My initial thought on posting was that $30 billion would not be enough, though the first read of actual per-mile costs, neglecting per MW-mile, seemed to suggest otherwise.)