So, trading away one's soul might be considered short sighted and there's a whole argument to be had with regards to the state preventing us from making short sighted decisions, so lets say that the desert rescuer was demanding the starving life savings or something.
It would certainly be a horrible person who would demand that much for saving a person's life. But if the only reason that this or other person was holding rescue patrols in the desert was that they were hoping to strike it rich exploiting lost souls, then as a society we either ought to allow this or use taxpayer money to fund our own rescue patrols.
And remember that as a laborer you're not in anything like this situation. There's a lot of charity out there and though this won't make your life pleasant it will make you far better off than starving in the Sahara. And there is more than one potential employer out there bidding for your labor. And you can see that the system works because very few jobs only pay the minimum wage. If we were somehow to get into a situation where there was only a single employer in the country than I'd say that at that point some sort of government intervention might be called for.