Looking for advice on the best way to allow user sites to upload audio files

I have a multi site and would like to allow my user sites to upload audio files to their site, but I am concerned about storage, especially when I have hundreds of sites. At this time, I am not even using a dedicated server, but will be upgrading soon.

My question: can you recommend an audio storage solution off my server? I have looked at SoundCloud and Microsoft One Drive and even YouTube. I would need to give them the ability to do it themselves without giving them the full code embed rights.

Thanks, Joe.