Coen,
We have the perfect solution, it is called Final Share. You can connect multiple users to one drive array and if you need to add more clients that is not a problem. If you run out of storage you can just daisy chain another drive array and we can set it up as volume two. This is the most cost effective way to have shared storage. If you could contact me directly at 714-374-4944 so I can go over some more details with you.
Sincerely,
John West