Since you'll want to be able to swap out those drives should one fail, you'll need another 24 drives as spares.
Good call Wolfshadw.
Ok, but I figured out a compromise. By adding 3 pci x4 sata controllers we can fit 13 drives in those hot swap slots (say that 3 times fast).
8 IBM 42D0410 300GB 15000 RPM 4Gb Fibre Channel Internal Hard Drive
1 Lenovo ThinkServer 67Y1385-BN 450GB 15000 RPM SAS 6Gb/s 3.5" BDL Hot-Swap Internal Hard Drive
4 Lenovo ThinkServer 67Y1386-BN 600GB 15000 RPM SAS 6Gb/s 3.5" BDL Hot-Swap Internal Hard Drive
And as the case can hold a cool 24 HDDs it fits them all like a champ.
Which brings us to a thrifty total of $49,090.98