How can I travel for cheap? (see details)

I would like to travel to a different country (I live in the U.S.) and do volunteer work this summer for a week or two. However, I don’t have a lot of cash and want to find a program that would not be too expensive. Any ideas? I looked up Habitat for Humanity but most of the international programs are at least $1500 for 10 days. It’s funny how expensive it is to volunteer.