Looking for Backup solution

I work for a small design studio. We have 5 Macs, and currently have half a dozen external hard disks for backup and archiving. A mix of time machine and manual copying. It's getting messy!

So we want a better solution. Something that will automatically backup all the computers and have enough capacity to store 3-4 years of work. Probably around 3-4TB. Something reliable, network-able and cost effective. The plan would be to have it stored in a fireproof safe in the basement.

Suggestions welcome, thanks.