Where I work we have a super fast SAN for our storage, with a giant cache, fiber everything, and separate channels for backups. The cost works out to something like $1k/GB. Beyond that we're perennially short on rack space, so there's a cost to buying new storage. I used to believe it would be cheaper for the company to add storage than to make me clean up my home directory, but I worked out the numbers one day and it's simply not the case.