Interesting idea. I think I'd prefer my funds to go to the raffle rather than be a straight donation, but that's just me. Other's will surely differ, or prefer to split their funds between the two.

Regardless, if you move forward with this idea, what about the idea of having ceramic chips/plaques made up? The folks placing their bets could choose a chip/plaque of the appropriate denomination and sign them or write their name on them with a sharpie marker. The larger plaques are plenty heavy and visible, and if you wanted to go with something bigger than a standard chip you could always start w/the 43mm variety.