Dont mix Scrypt and Keccak mining, an rig that gives 2800Khash scrypt, will give roughly 1200-1300 Keccak.
That link has 4x Sapphire 280X Vapor-X, i have a couple of those and they give around 350Mhash each on Keccak, and 750Khash with scrypt
(Note that ebay add doesnt seem right, my GOD that rig will overheat with so little space between cards.)

max.nut2pools.com