How Backup External Hard Drive?

I am using my Mac Mini in my home theater to play my backed up dvd collection from an external hard drive (1 TB). The drive is almost full and I have been thinking about the possibility of the drive failing and losing all of the movies that I have backed up. I thought about changing to a networked RAID system or NAS but they are somewhat expensive. I thought about backing them up through time machine but didn't know if that was the best option. Any ideas?