Here is the difference. The left is the estimate I received at time of booking. The right is the final receipt after the rental was returned. All the green items match up and were requested, including the fuel refill option (which I now know was a rip off but whatever I usually do that anyway). The charges in black font on the right side were not requested by me nor were they included in the estimate.
It's very clear this is just sleezy, vegas-hotel style pricing to make it seem like it's a much better deal than it really is. I requested a refund on the items I did not authorize so we'll see how it goes. But my advice is get the declaration of charges at the time of the rental (right before you drive off with the car). If I had that up front, I would have been able to contest right away.
UPDATE: National did refund the items I contested. All is well but remember to always look at your bill.