SAR people may largely be volunteers, but helicopters have fairly expensive operational costs. In time-sensitive situations, it is better to have two way communications (because it keeps SAR as inexpensive as possible). See my sister comment for my wife's experience.
In our case, our org (Norwegian Red Cross) buy the equipment using sponsor money and the like. Then we get reimbursed by the government for using them in SAR operations.
It works well enough for us to have maybe 4 snowmobiles, 2 6-wheel ATV's, a 4 person rope rescue kit, 10 TETRA phones and a car in addition to various medical equipment.