For its "M" Club members only, mwave.com offers the refurbished Iomega Prestige 250GB Portable USB 2.0 External Hard Drive, model no. 34277, for $29.99 plus $4.99 for shipping, ("M" Club membership is free; click here to sign up.) That's $0.14/GB and $27 under the the lowest total price we could find for a new one. It has an 8MB cache and runs at 5400 rpm.
A 1-year warranty applies, although it's unclear who supports it.