Wirelessly posted (BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
Whenever you have a rate that does not include unlimited mileage, it is essential that you check the car's odometer at the beginning of the rental to make sure that the reading agrees with what is stated on your rental agreement.
I'm afraid that you just learned a very expensive lesson.
What explanation did the rental location give for failing to honor the price on your reservation? And what did Hertz customer service tell you when you complained about the failure to honor the price in your reservation?