The circumstances are not entirely clear from your posting. But here's a good rule of thumb: any supposed "volunteer" organization that asks the volunteer to pay *anything*--and this includes plane fare--is a potential scam operation. Volunteering means that you are contributing your experience and a hunk of your life--this is YOUR contribution. Transportation, housing, food, etc., should be THEIR responsibility. (I hate to shout with caps, but I can't seem to enable italics.)

As the cliche goes, be warned!