I'd say with the person who took the initial risk. If you don't stop and think, "gee, if I do this, maybe I might get lost or hurt, am I adequately prepared, and willing to face the consequences if something does go wrong?" That's how most ventures in life go anyways.

I am really getting stuck on why the concept of responsibility for one's own actions is so elusive here. Surely people must realize that when they put themselves in a bad situation, they really only have themselves to blame for it. The availability/economy of independent aid should never be a factor in decision making of whether the risk is acceptable or not. That is illegitimately trying to convey the burden of responsibility onto someone with little/no vested interest in the outcome of your pursuit of happiness. Should you succeed and overcome the risk, they receive no benefit, so why on earth should they share in the blame for something they really have no say about in the first place, other than caveat emptor?

I would think an adventurer should be more hesitant to even consider taking an unnecessary risk if they are not prepared to face the worst reasonable outcome. The cost of rescue should not even be a deciding factor whether to go or not. If a life is lost because the person in trouble was unprepared, what difference does it make what the cost of rescue might be? They made a mistake. Cause and effect begins and ends with the person initiating the action.

Take any chance of independent rescue or aid out of the equation, then make the decision and any planning based on that limitation. Then you don't have to really worry too much about what it might or might not cost you.