I started a new thread with instructions on how to make a script run as a cron job. You can check it out and let me know if it works for you. I figured it out from the scripts basic you posted.All - I am no script guru and currently do not have any cron jobs configured for backing up my plug-ins in any way. I am sure a very nice script could be written to handle this process but I do not currently have time to tinker with this.
Maybe someone with more scripting knowledge would be able to whip one together that will backup the config/database for the plugins and clean up old backups.