If the coast guard or national park service or local agencies consider you "negligent" here you will probably get billed. Or if the 911 call was frivolous.I guess it's region- and country-specific. I can pretty much guarantee you that if you're lost at sea here, or need a rescue of any kind, the bill you receive will be exactly 0.00 USD
For instance, you set off hiking into the grand canyon in flip flops, couldn't walk out due to blisters, and then called for a rescue. If you break your ankle hiking or skiing in the French alps and need extraction you will get a bill - even if you aren't negligent.
Saying rescue is always free is not accurate.