I found the same issue with National being a lot higher than their competitors.
I've been a long Enterprise user (being "underage" USAA waives under 25) and wanted to give National a try when I fly into DCA in a week. Though compared to all their competitors, their rates were much higher. Not to mention the tacked on airport fees etc were higher.
I brought this up to their Twitter relations team and they agreed with me after sending the breakdown. They forwarded it to their DCA branch, but as usual. They couldn't do anything about it and apologized.