Actually, as CMKRNL put in, the price of DDR2 seems to be 50% more expansive than the 325%Hz counterpart. But, that's public information. we don't know how much Ati pays for it's RAM and Nvidia's.
Sorry, I should have made it clear. Those were nVidia's volume prices as of about 2 months ago. The percentage delta may have changed to some degree since then.