My D is on a gap year as are several of her friends. She had a paid job for a while to earn some money and is now abroad working on a farm through http://wwoof.net/ because she’s interested in environmental science.
Another of her friends is teaching English in Spain. Another good volunteer program is the Student Conservation Association.
It has been a great experience for my D so far. I’d recommend it highly and there are many opportunities besides the high priced programs.