Unfortunately, it isn't uncommon for criminals to cause damage in the course of committing their crimes. I don't know if it is normal to hold them financially liable for that. And I don't know if it matters that some of the crimes ARE the damages they wrought--they weren't just incidental. I'm all in favor of holding these thugs accountable in any way that's legal.
Even if a court ruled that they were liable I doubt the government would be able to collect anything from the perpetrators. Media reports, assuming them to be reliable, indicated that a good many of the occupiers receive public assistance and/or were typically very low wage earners. Without paychecks to garnish or assets to seize the cost of pursuing a court judgment would likely be more expensive than just eating the cost.
$4M? I will do it for $1M. "$2 million of that came during the takeover and included paying to move the refuge's 17 employees out of town for safety to live at government expense in hotels for weeks." - (my emphasis) They were in town. Not in the park. The occupiers did not threaten those individuals. But, let's say this was necessary. 17 people * 2.5 for family, two months (which it was not that long), $100/night hotel (which it does not have to be) so that would be 17*2.5*60*$100 or $255,000. What was the other $1.75 million spent on? Even if they gave them $100/day food money that would still be only half million. where is the rest went? But, $2M needed for the actual clean-up... $2M. Last year, in the same refuge 5,301 acres were treated at the cost of $216,735. Something is just not adding up, or someone needs a new pair of shoes...
Oh I bet a $100,000 would clean it up. Why did they move people out of town? Also if you read the article very carefully you'll see it say "Upgrade" the place.