External Enclosure that can hold multiple drives?

I'm looking for exactly what the title says. I've seen some but they run for a few hundred and I'm sure one must exist that's cheaper... Anyone seen anything like this for a decent price?

For the record, I'm looking for the kind that pools the storage, ie if I put in two 250gb drives I'd have a 500gb drive, not the kind that backs up the drives.

 

Thanks! I guess there's nothing horrendously cheap that does this then, ha. Thanks though!