Kevin Costner is facing a nightmare $100 million bill after his vanity project, the Western movie saga Horizon, flopped at the box office, according to insiders who say he’s being forced to cash in a trove of precious assets to pay the massive debt. As RadarOnline.com previously reported, the Yellowstone star, 69, mortgaged his stunning 10-acre Santa Barbara ranch to help fund the ambitious four-part big-screen epic. Part one only brought in $11 million on opening weekend, and part two has been pulled from its original August release. Now, sources claimed he would have to cough up some serious…
