As several have suggested Bundy just fight them in court, I ask would that be a fair fight??? Even financially possible?? So could a rancher afford to pay seriously expensive attorneys to go into a Federal court in front of a federal judge and battle a federal agency and expect a fair shake?? That's just naïve.
People challenge federal agencies in federal courts literally (almost) everyday. Some of them win. Some of them settle. Some of them lose.
The problem is that Bundy doesn't have any sort of constitutional/legal framework with which he can make a credible case. Just because he can't win in court doesn't mean that the deck is stacked against him--that's just how our legal tradition has worked for the past few hundred years.