ARAID 2000 SATA RAID 1 Dual Disk Data Storage/ Back-up Controller was the first such device I looked at, but I found a competing product.
As of the date of this post the ARAID 2000 can be bought at Carday Supply in for $390 plus $46 for an extra tray.
Carday Supply also carries a similar product called the Stardom-2600, which is $332 plus $24 for extra tray.
SyneRAID.com Data Storage Management Solutions also carries the Stardom line.
PC-pitstop has the Stardom 2600 for $269 plus $37.50 for extra tray. They also have Western Digital 160GB SATA-II drives for $78 each (or bottom end Maxtor 80gb SATA HD w/8mb cache, 6Y080M0 for $55 each). This solution would mean a cage, extra tray and 3 HDDs would be $540 plus shipping, or with cheaper HDDs $471.
Both of these brands allow two harddrives, each in two a removable drawer, that mirror each other. The Raid hardware is included in the case so the computer only sees one harddrive.
Strangely, the device will copy a hard drive without connection to a computer if it has the right power supplied.
Nice NETGEAR ProSafe JGS516 Gigabyte 16 Port Switch for $199 with rebate at Egghead.