> this estimate is never honored by dealers.

The "build your car" tools on the websites always represent the "as low as" price. It assumes all possible rebates, many of which you aren't eligible for. If you were a military veteran who recently graduated college with great credit and an account at a credit union with a pre-existing arrangement with that dealership, and are also trading in a same-brand car while trying to purchase a model with flagging sales, then tada, you can easily get the "as advertised" price.

Edit: this is incorrect. See replies.