Search and rescue in Montana is largely a public service, funded by taxpayers and carried out mostly by volunteers. But once a helicopter enters the airspace, the economics can change dramatically. Federal law has given people with health insurance more protection from surprise bills, but the particulars of backcountry rescue — and different insurance plans — remain confusing enough that even officials acknowledge there’s no simple answer to the question an injured trekker faced on Froze-to-Death Plateau.