Backpacking in the backcountry is a risk and the participants should assume they are solely responsible for their own rescue and that there is a possibility that nobody will come rescue them. This point is made clear over and over in the video that comes with a Grand Canyon's backcountry permit. If rescue does come, it should be the resposibility of the participant for payment, period.

Diving and backpacking are similar in that people are voluntarily participating in an activity that has some inherant risk. A lot of diving takes place in a foreign country, where it's possible that no treatment will be offered without pre-payment or a verifiable guarantee, at a minimum. Dive accidents often require very expensive, low altitude evacuation, to reach the nearest recompression chamber that's required. There are a couple of world-recognized agencies (D.A.N. and P.A.D.I to name a couple) that offer yearly insurance policies to cover these types of expenses. My experience is that a good percentage of divers carry this type of insurance and I would never dive without it.

I'm not sure if anything like this exist for backpacking but I do know that many travel insurance policies offer medical evacuation coverage.