Where does the money come from?
From selling the donated computer time, in bulk, to science and industry.
One PC isn't much use but, if enough of them work together, they can be very useful indeed. The Charity Engine grid is hired to companies, universities and researchers as the world's cheapest, greenest - and most ethical - supercomputer.
And because Charity Engine only uses spare resources that would otherwise be wasted, it generates far more money for the charities and prize draws than it costs to run.