What is there to dispute? Possibly the fact that the violation happened *over a year ago*. The OP did not state whether Hertz or the local municipality contacted him prior to today to let him know about the violation. If they had, it's likely it could have been resolved for less than $820, which sounds like the cost of the violation, plus late penalties, plus possibly an administrative fee. If it were me and this was the first notification I got for the violation, then I would dispute it simply based on the fact they did not notify the OP in a timely manner of the violation.

There has to be some expectation that issues like this will be handled promptly, and by anyone's measure, a year and a few months after the violation was committed would not be considered reasonable.