Frequently organising DBA events that form part of larger conventions I'm often restricted by what the convention organisers will provide in the way of prizes. It is made worse by people not organising their registrations early.
When I have any control over the prizes I prefer to see more smaller prizes than large ones. I feel this provides less reason to focus on competive play and more social interaction. A voucher or discount to an Ancients figure manufacturer is ideal. A full unpainted DBA army, perhaps as a random draw, would be a bonus, but seldom achievable.
For many of our local events where there is no entry fee the only prize is fame, and perhaps having your name on a trophy at least until the next event. One of the other DBA organisers here has been particularly efficient in providing, via our local club, such recognition.