Using Cron and scripts to do a backup

[wags22]

I want to set up a semi-automatic backup of newly added files. My intent is to set up a script that will check all files in a directory and subdirectories, compare when they were created to a set date (date of last backup, and at this point, starting date of files being uploaded), make a list of files that need to be backed up. Then from that list select files that the total backup will be less than a set size (4.5 GB - DVD disk size). If the total size is not up to the required amount, nothing happens, once the total size reaches the required level, it will prompt me to put in a disk and start the backup.

I know that I would need to use find and grep to accomplish this, but I'm not sure how to setup the script to accomplish what I want.

Any help would be greatly appreciated.

Please note: I want the backup to be of new files only, not a complete backup of all files.

Thanks,
Wags