If you are going down the cash route with no vouchers, I think you could do it for $41 and 3,200 points with the following steps:
(1) Do the quiz;
(2) Offset a domestic flight for less than a buck (e.g. Syd-Mel @ $0.98);
(3) Donate to a charity @ 3,200 points (I can't seem to find a cash...