Chronosync is a very nice product, but as far as I know, it's only Mac to Mac, so your backup server would need to be a Mac.
rsync + cron may be a cheaper and more flexible option, you could rsync to a local and a remote server and possibly to an online backup service (not sure about that though, not looked into online backups). Using OS X logout hooks you could even get the rsync to sync before shutting down (the users would need to understand that this happens and not try and force power off), for a nice GUI try iHook.
If they are looking after it after you have set it up, I'd say stick with Chronosync, it can get expensive (probably not as much as 3K though
) and it's not as flexible as rsync, but much, MUCH more user friendly!