I find it kind of odd that there are so many people surprised over the money issue. Remember, Disney couldn't afford Robin Williams for the original movie; he actually agreed to take a major pay cut in order to do it though, on the conditions that they not use his voice recordings for anything outside the movie, and that they not give his character top billing/have him be the primary focus of advertising. Both of which they did anyways. That's why he didn't voice Genie in the second movie, because he and the company had had a falling out over them ignoring his conditions. It was only after a public apology that he agreed to do the third one. Honestly, for how few lines Genie would get in a KH video game, I'm not surprised Disney wouldn't want to try to broach the subject with him. I just probably wouldn't be worth it for them, sadly.
...Of course, I never really liked Castallaneta as Genie anyhow. I mean, I love him as a voice actor, and he's brilliant, but he was always too over-the-top as Genie for me (which I suspect was more of a directing choice). I think the problem is that no one is able to play the character with the same, huge vocal range Williams was able to. Also, it seems like they always go for the lower register when Genie's 'normal' speaking voice is actually a little higher.