Trans. Intl. offers the Toshiba 500GB Serial ATA 6Gb/s 3.5" Internal Hard Drive
, model no. DT01ACA050, for $48
for shipping ($0.11/GB). That's the lowest total price we could find by $6, outside of the price below. It runs at 7200 rpm and features a 32MB cache.
A close price: Memoryonly.com via eBay has it for $56.99 with free shipping.