Like anything on sale, the sale is only as good as your need for it. In this case, the last minute specials don't benefit you based on your needs. I know its disappointing, but the only reason National (or anyone for that matter) offers a discount from their published prices is to attract customers. Based on their needs, they must find that your business is not as valuable based on the criteria in which you are trying to rent or that they do not need to offer a discount based on that criteria.