link: http://www.ebay.com/itm/4XF0F28766-ThinkServer-2-5-SATA-SSD-Cage-with-SATA-Interposers/161880154174
Showing buyout (quantity available) for $75 (should be a pair of them/4 drives, per description.
Of course, I bought a while back and paid retail, 'cause I couldn't find a cheaper...