I'm a student, and I don't live in the US, therefore, I wouldn't have a lot of methods to pay [if any are available, which I don't think there are], I would have to disagree with paying.
I mean, this game made listening to music better. It made music fun. And I'd be really pissed to just find out that I have to pay $10 or something to play this. I would be all 'Oh shit what now?' and that would be sad.
Though I'm not saying that you shouldn't get a cent for your work, I'm still opposed to it.
If you really want to, you can make an offline version [please do this], and make us pay for accounts so we can post our scores to the server.
Also, muffins [please do this].