An interesting option I hadn't seen until very recently:
http://www.extremetech.com/article2/0,1697,2018463,00.asp
http://www.newegg.com/Product/Product.asp?Item=N82E16816133001
Not particularly fast (99MB/sec was the fastest number I saw
in the review). But if you need $6TB for $3k it looks pretty
attractive.