I am not a content provider but my idea for a cheaper solution to a hard drive may be a thumb drive like this?
http://www.google.com/products/catal...d=0CJcBEOUNMAQ
If you are only searching for a downloadable way then maybe split the content into multiple 1 or 2 gig segments and set up an account per customer via ftp. Ive ordered small sets for site design and they basically have an ftp account for me that has my old files and whatever new ones i purchase, i downloaded like a gigs worth without any issues, and can d/l or re d/l it on whenever. No idea how long hey actually keep the stuff up there but it seems like a fairly long time. That way seems kind of like a pain though, i say thumb drives lol.
Best of luck =D