The usual solution to this problem, when you're short on cash and need to push out a lot of gigabytes to a lot of people, is to put up a torrent. They're not just for piracy!
(Fun fact: if you host files on Amazon S3, it will also generate a torrent file and handle the seeding and tracking.)
I kept pushing that solution too, largely because I love the "here's another legal reason for torrent technology" proof that it gives, but it was important to datassette to be able to directly stream from the site and that isn't possible with a torrent.
Yes, both a magnet link and a direct link should be offered, and probably will be soon.
uTorrent allows streams in torrents. Interesting that they haven't made it a bigger feature, this has a large potential if it becomes a bigger part of the torrenting user interface. People complain that this stream download is bad for the peer cloud, but it could work very well if there's a single big server or two backing everything up- at the same time, taking a lot of bandwidth pressure off those servers.
(Fun fact: if you host files on Amazon S3, it will also generate a torrent file and handle the seeding and tracking.)