Ocean Technology via Amazon offers the Unitek Serial ATA Dual Bay USB 3.0 Hard Drive Duplicator in Rose Gold for $37.99. Coupon code "WTT5Q9QE" drops it to $17.10. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $10.25.) That's the lowest price we could find by $23. It supports 2.5" or 3.5" serial ATA I, II, or III hard drives up to 8TB and features offline cloning.

Update: It now includes free shipping with no requirement for Prime.