It's a non profit association that organises and pays for this, with the ok of the courts, etc. They get a daily stipped'md lf 16€ each, for food and lodging. The "offender" also gets 3€ per day as pocket money, so they can buy cigarettes, or candy, depending on their age.
With 16€ a day, kt's difficult to explain that "donativo" does not mean "free".
There is also budget for visiting monuments, museums, etc. The association pays for the backpack, clothes, etc the "offender" needs. In the case lf the boy I walked along woth for a few days, it had cost about 400€ I'm told.