Did you mean Aug 13th of 2013, Sept. 13th, 2012 or something different?

I did a quick orbitz check of orlando for 7 days starting on Sept. 13, 2012 and could see as low as $60/week by Payless for their smallest car. For full size, Economy car rental had the lowest with $80/week.

So I have to assume you want different dates than Sept. 13th as prices are much, much lower than your seeing or Aug. 13th, 2013 as I'm not sure that most car rental agencies will even let you book that far out.