For young people looking to volunteer on a gap style project but without ebough money to fund themselves should take a look at Platform 2
Platform 2 is a fantastic opportunity for 18-25 year olds from low income families to go on a free 10 week trip to a developing country to work on community led projects. It is Government funded and run by Christian Aid in collaboration with BUNAC and Islamic Relief.
Here is a video involving young people who've already responded to the scheme.
If you would like more information please check out their website on http://www.myplatform2.com/ which includes the application form, stories from volunteers on the trips at the moment and more.