It's not just for luxury cars, either
Take the entire MINI product lineup, for example. Each model is customizable down to the most minuscule details, from the color and texture of side-view mirror caps (seriously), to the contrasting interior hue. According to MINI, there are millions, if not billions, of permutations to spec out the 2017 MINI Cooper (and Cooper S) Convertible. You want your six-speed manual Cooper Convertible in Lapisluxury Blue over Malt Brown Chesterfield leather with a tasteful chrome accent package? That'll cost you a hair over $30,000 -- or about as much as a loaded Honda Accord will run you from the dealer's lot... assuming you can differentiate it from the crowd.
Start by going to the car manufacturer's website and click on that little "Build It Now" button. Figure out which options make sense for you, then go to the dealership and check those options out firsthand -- you probably won't find a car with all of them, but you can try the seats of one and the stereo in another. When you've made up your mind, skip the salesmen entirely and sit down with (or even email) the sales manager with your order and how much you're willing to pay.
Custom ordering is also cheaper, if you're smart about it
Let's say you want the New Hotness Coupe 27B, and the ones on the lot have navigation and the high-end stereo, but no moonroof. And you really, really want that moonroof, way more than you want the fancy-ass stereo. When you place your order for exactly what you want and nothing more, you'd be surprised how much just a little restraint can wind up saving you -- it's often several thousand dollars.
Not buying off the lot also helps you to seize back some of the power in the whole buying process; just because you custom order a car doesn't mean you have to pay attention to that "suggested price" on the window sticker. The art of bargaining and deal-making is a bit old school, but consumers have more resources than ever at their disposal -- from TrueCar price guarantees, to sites that expose invoice prices and subsequent dealer markup. Even if you're not an experienced negotiator, showing up with your well-researched offer price will give you the upper hand. It lets them know you're serious and helps cut through the inevitable bullshit some dealers like to throw at you if they think you're unprepared.