At the end of the event there will be one winner of each prize.
People purchase chance tickets to use.
If they are interested in winning an item, they put a chance ticket in the box designated for that item. To improve their chances of winning, they can put more than one chance ticket in any of the boxes. The funds raised are exactly the total amount spent by people on the chance tickets, since the prizes were donated. Solicit businesses for prizes. You pay only shipping and handling.