Money for Voluntary Work

[Harry79]

i want to do voluntary work abroad but it's very expensive. i was planning to do a sponsored run or something to raise money for the trip but i don't know the legal ins & outs of this.
would i have to fill in tax forms or anything? the voluntary placement costs around �900 & the flights would be around �700 & i wanted to hopefully raise enough to cover as much of this as possible.
does anyone have any cunning ideas? or advice?
thank you :-)