Hope Si doesn't mind me stepping in here
As my missus has buggered off and left me to my own devices for a couple weeks, i'm forming a new relationship with my computer (and maps of Chad !!)
What i suggested to Si was he use the UK National Lottery as an independent decision maker, it runs twice per week, and one of the features is a bonus ball. So one number from 49 can be transparently selected as the winner i.e. 49 tickets to be sold.
At USD$25 a ticket, after PayPal fees and shipping to the winner, approx. USD$1150 will be the net proceeds to the charity, pretty damn good.
15 members so far have said they would buy a ticket on the poll at the top of the forum, to kick things up a gear i personally will take 3 tickets, perhaps others would consider multiple plays too (wink, wink, nudge, nudge).