Just wanted everyone to know, for my 3 day rental that I'm picking up on Friday, I originally had the "67" code for my midsize vehicle. The total was $87.
I just went to the "Last minute specials" page on National's website. Using that link and code, and the visa one day free coupon (mou$e$aver$) the total came to $66.
So, turns out, the last minute special is a better deal. YMMV, but check that link 2-3 days before you leave--last week when I checked it, the "Last minute special" was still more expensive than "67".