This may be somewhat unconventional, but in my experience you aren't going to beat the big dogs when it comes to storage, in terms of cost. Managing RAID arrays is something that in my experience should be avoided if possible. Everything is moving towards the cloud, I think it would make sense that this does as well.

What about having each storage server have an aws or google apps account, pulling in data as needed from a secure location we do not have to manage, that costs around $5/mo per seat for unlimited storage?