Replying to Using music legally?

I am working on a video for a school project, and my teacher wants us to be able to show them on public access. To do this, we have to have the rights/permission. I haven't been able to find anything on any creative commons sites, and I have tried emailing the record company for RJD2 (I want to use ghostwriter, still waiting to hear back), but I need other music as well. She just told us this halfway into the project, but does anyone know where I can buy (reasonably priced) the rights to use a song that I already know for non-commercial interest, essentially itunes for non-commercial use? I can find plenty of sites giving out music for free, the problem is that they don't have much well known stuff. Also, will buying it in itunes count (I'm assuming it won't)? If it is by pretty lights or a similar group where they give out the music free, is it fine to use non-commercially? Any help would be appreciated. Thanks