I am using Amazon S3 file storage and some software (S3 Backup (www.maluke.com)) to backup ~300GB of digital media. Amazon's off-site, always on, fully fault tolerant storage costs me about $23/mo. + my internet connection. The major downside is that you need to download or upload your content. It took almost 2 mos to do my first complete backup due to my slow uplink.
As far as on-site storage, the only option is to stay current with technology, and rely on common or open standards where possible. For example, don't encode your video with an obscure manufacturer's codec. This often means you will need to pre-process backups, or dedicate time for conversion at some periodic interval. Every time you upgrade your OS, you should recover your files and test them. If there are any compatibility issues or technology upgrades, then you should convert to new media at that time.
When you burn media, you need to burn 3 copies - keep at least one off site. This way, if one goes bad, you have a third copy to which you can compare 1 and 2, telling you which is out of synch.