THIS CAVE ENTRANCE IS VERY PRETTY and I was guessing the cave itself cost a bundle, but Joe Bob Hitchcock says it was deceptively inexpensive to dig. See next photo for why.
THE CAVE ITSELF wasn't bored into the mountainside -- they dug it trench-fashion with a neighbor's D8 Cat. Then they roofed it over, lined the insides with gunnite, poured the floor and earthed over the roof. Tada!