EZ-Backup

Per computer:
$5.50/mo
(First 18 GB, compressed)

http://www.it.cornell.edu/services/ezbackup/fees/

Default setting is to backup full computer, including the OS, which makes for a larger backup and thus potentially more expensive.
But the most cost-effective method will requiring carefully and accurately focusing backup on just user's unique docs, not full OS.

File server

Per group:
$9 for 150GB
$30 for 500GB
$60 for 1TB (onwards)

http://www.it.cornell.edu/services/sharedfile/fees.cfm

Service backs up all files there via EZ-Backup at no additional cost.
Versioning (access to prior versions and deleted files) is available, and obviously takes up some  of the allocated space (~20%).
Set up private folders for each member. By default, can't see each others files.
Has capacity for shared folders, if sharing is desired.
CIFS are Windows and Mac-friendly.
Accessible from off-campus via VPN.
NetID-based so usernames and password are easy to remember.

Box.com

Free to CU members, up to 10GB
More data, via formal request.

http://www.it.cornell.edu/services/box/about.cfm

Good for working files. Good for sharing, including to your own, other computers. Limited space.
Individual file size limit is 2GB.
Limits on file names and path lengths.
Cornell-contracted. Use and rights governed differently than with your group's private DropBox.com accounts, for example.
More space may be available to individuals; contact ChemIT to explore this option.
Service stores prior versions of files, and in most cases also deleted files.
Consider backing up files in case account gets hacked or of a bad internal actor.
NetID-based so usernames and password are easy to remember.