You would have to go with SAS to get 15k rpm. An MD3000 from Dell supports 15 drives. If you went with 300GB SAS drives at 15k, it would only be 4.5TB in a 3U rackmount enclosure. This would be expandable up to 13.5 (3 x 4.5TB enclosures), but that is with 2 additional enclosures for a total of 9U rack space. If you were able to compromise the speed and go with SATA at 7,200 rpm, you could put 15TB into that one 3U enclosure. We get them for around $16,000. I don't know if that would fit into your "Tight Budget". I've had alot of success with these.