My middle one wanted to go on a camp organised by one of the local churches. As it was run by volunteers and they 'camped' in a local school, the cost was kept to a minimum. Nevertheless, it was more than we could afford living as we did at below the poverty line. He begged and pleaded and said he would pay for himself - the cost and some pocket money. We agreed that, if he saved enough, we would pay for the transport to the pick up point. This was quite expensive as we lived on an island so it meant a ferry crossing for him and a parent, then train fares but we decided that if he could make the effort we could help. He asked for money for birthday and Christmas presents and every penny went towards the holiday. Most of his pocket money was saved and he did odd jobs to earn extra.
He loved every minute and went three years running.