Talk of building a cutting-edge train tunnel under the New River gained steam this week, with billionaire Elon Musk’s Boring Co. saying it would cost only $10 million to $20 million per mile. That’s a far cry from state estimates of $1 billion per mile, said Fort Lauderdale Mayor Dean Trantalis, who met with Boring Co. executives on Monday and will be sitting in on another Zoom chat set up for .