SEAGATE 640GB Portable Notebook Hard Drive: $80
Buy a $25 off $75 coupon from ebay or ejunkie, the cost is around $5 (I see the cheapest is $3.50 from Buy It Now category, if you bidder,maybe cheaper but will need time).
$80 - ($25 - $5) = $60
Plus Tax
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* 640GB
* 5400 RPM performance
* Plug n' play - no software to install
* USB powered
* Automatically recognized by Windows
* Simply drag and drop to save files
* Built-in power management for energy-efficient operation
* Two-year limited warranty