You don't need to backup 300 gb on a nightly basis.
From your description,the data should be static for the most part.
You run a differential nightly and a full once a week.
If yhey have the money ,you set up a disk to disk to tape backup using something like Backup Exec 11d.
750 gig drives RAIDed set up as iSCIi targets are cheap these days and the use of eSATA is another method of cheap, fast, efficent backup to disk.