Well, if whoever will be the champion can get 100 million dollars, who wouldn't enter?
If Webby wins the pageant, she can share some of them with her family and Scrooge can use the money to build a Duckburg opera house or a Duckburg theatre.
If Gandra wins, she can enlarge her science experimental limit. Especially, she and Fenton can rebuild the Gizmocloud that Bradford had it shuted down before he and F.O.W.L. got defuncted.
If Daisy wins, like almost everyone believes she will, she will share with her "family" (The "family" means Donald, May, June and Daisy herself), although they're not married yet. By the way, I wonder how will she be appalled if she finds out May and June's backgrounds.
But for Magica, Della, Lena, Goldie and other contestants? I was wondering how would they spend the prize if one of them wins...