I would pay $100 to guarantee Banjo & Kazooie, just because I think they're the most deserving characters with the least chance of actually making it in, but I somehow doubt Nintendo is going to jump into negotiations with Microsoft just because some random guy from the US offered them a whole hundred bucks
Other characters I would considering paying for, in no particular order: Paper Mario, Tetra, Little Mac, Prince Fluff, Krystal, Tactician/Robin, Claus, Isaac, Takamaru, Geno, Bomberman, Quote, Gilius Thunderhead, and just for the hell of it, Roger Jr. from Tekken, because kickboxing Kangaroo mother/son duo, why not!