Shared storage is a way to virtualize storage. Use a shared storage device (a storage area network) like a Fibre Channel or iSCSI array, and never buy a hard drive in a server again. Just like virtualization allows you to better utilize the servers you already have, shared storage lets you better use the hard drives you use. In fact, inventive use of shared storage lets you better use the hard drives you may already have in excess servers.
If you have some underutilized servers laying around with lots of internal drives, you can “roll your own” shared storage with shared storage software like OpenFiler. Software like OpenFiler allows you to reuse a server with internal drives and “make” it into a iSCSI storage array. OpenFiler is basically a tweaked Linux distribution with a focus on making a shared storage appliance, it’s as easy to load as Linux is. (I think Linux is easy, but I use it all the time. Even if you don’t regularly use Linux, it’s not so hard. Really.)
So don’t say “I can’t afford shared storage”. You can’t afford NOT to.