The question surely isn't "As cheaply as possible", after all, you could just delete it - that'd be cheap. Tape is still the cheapest, reliable option, and you

The question surely isn't "As cheaply as possible", after all, you could just delete it - that'd be cheap. Tape is still the cheapest, reliable option, and your main options are Quantum, IBM, and Oracle (Sun). The Quantum Scalar i500 can store up to 600TB of data, and is relatively cheap, or you could buy 4 or 5 smaller models and use tape management software to track where the data is.