you can look at the "HP proliant 40L micro server"
it's pretty cheap and pops up at $199 quite often.

I got one and have 7 HDD on it. and run Win7 ultimate x64 as my file server.
no redundancy as I just set it as a regular desktop with filesharing on the drives.

but it is like a regular computer, you can put linux or what ever os/setting u want.