My Terabyte's of storage is in a 'SCSI' raid array, very very expensive to buy. Chassis around £400-£1,600 (this depends on then number of drive bays), disks anything from £90-£1,000 each. These will only be available from certain suppliers, mainly web based.
This can be made more affordable by adding a 'SCSI' card (Adaptec are the best I've found) to the PC and using a boxed external 'SCSI' drive. The external 'SCSI' drive plugs into the back of the card, externally to the PC via a cable.
Unfortunately price gets you data transfer speed when it comes to the cards, 20Mbps will cost around £60, whilst 320 Mbps will set him back around £200. Disks obviously vary dependant, yet again on cost.
These can be brought on the high street at your PC World's, Office World's, Staples etc, costs are better when brought 'Online'. I saved a fortune when I built my PC recently, by using a company called 'NOVATECH' http://www.novatech.co.uk/novatech/home.html
Need any further help, give the "Anorak" a shout!!!