The Apple Xserve RAID box is a rather good value: 3.5TB for US$11K. FibreChannel connect it to a pair of 1U Xserve servers to export NFS and CIFS. Or use FreeBSD-5.x for NFS with Samba for CIFS, and get NetApp-style snapshots:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/snapshots.html
I haven't done this but would love to put my hands on an Xserve RAID box to front with FreeBSD-5.