Looking for an inexpensive, good raid 5 disk array

Okay, I'm looking at replacing an old terrastation that's full and to consolidate my other external drives into something with some redundancy (almost just bought a few 2TB drives cheap before i remembered that there would be no redundancy).

Hoping to get 6GB after hardware raid 5 overhead (so 4x2TB).

Either firewire 800 or gigabit ethernet interface. Mac compatible (of course).

Not looking at breaking the bank, so can add drives myself if needed.

Any suggestions?