GPI is a charity group. They have orphanages in Africa and India. They also use their 747-SP to take volunteers to places around the world in need of medical help. They sent Dr.'s and nurses to help the tsunami victims. From what I have heard a lot of the crews are former United pilots. They told me they have no problem finding qualified pilots, but current and qualified flight engineers is another story. They are planning a trip right now, but can't find an engineer. I am non-current so I couldn't help (I'm also in ground school so I can't exactly just leave now either). I'm also not sure how they get you to the airplane (it's in India right now). I hope this little bit of info helps.
I am not sure who the major contributors are. They have had some of the maint. and checks donated to them. I can only imagine how many millions it takes to get a D check. It's probably like other charities and depends on it's volunteers to find financing/donations/more volunteers.