a typical enterprise spec for a server is a 8 port RAID hardware raid card; hosting RAID 1 SAS drives for OS and RAID 5 SAS for the data (with hot spare).
the IO system alone would be:
LSI 8 port PCIe 8x controller: $650
two seagate 146GB SAS @15K RPM for OS: $400
four seagate 300GB SAS @15K RPM for data: $2000 <-- this gives you close to 1TB storage
that brings your storage system to $3050 (ncix)
it's fair to say a proper server only performs as well as it's storage system. What was your budget again?