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World's most expensive car accessories

Among the list of car accessories, this one tops the lot. But it turns out Bentley is not alone charging big bucks for basic items.

And you thought $150 for floor mats was a bit rich.

British brand Bentley has unveiled the world's most expensive car accessory: a built-in Breitling clock for the dashboard.

At almost $300,000 dollars -- on top of the car's $450,000 price tag -- it's enough to buy a brand-new Porsche, with some change.

Proving that some buyers do have more money than sense, there is already a digital clock in the car's instrument display.

The Breitling accessory is an option on the world's most expensive SUV, the new Bentley Bentayga, due in Australian showrooms in April.

The special timepiece is made of gold and uses diamonds for the index.

Bentley claims Breitling can only build four of these particular in-car clocks each year, and two are already sold.

Bentley would not disclose if any Australian customers had ordered the special timepiece, which is made of gold and uses diamonds for the index.

Although it may never see more than a gravel driveway, the Bentley was designed to overshadow the former king off-the-road, the Range Rover Autobiography, which now seems like a bargain at $342,000.

In addition to its expensive options list, the Bentley promises to be the fastest SUV in the world, with a top speed of 301km/h.

It's powered by a twin-turbo 6.0-litre W12 ('W' is correct, they are two V6s mounted back-to-back to form the shape of a 'W' rather than a ‘V') that will be able to pass almost anything except a petrol station.

Bentley is not alone when it comes to charging big bucks for basic items.

Ferrari charges $19,000 for racing stripes on its sports-cars, and another $19,000 for two-tone paint.

A rear camera -- now standard on a $14,990 Honda Jazz and $15,990 Toyota Yaris hatchback -- is $4990 extra on the $470,000 Ferrari 488 GTB and a staggering $9600 extra on the $795,000 Lamborghini Aventador V12, a car famous for "scissor" doors that open vertically.

The dearest options on the latest Holden Commodore include a "racing stripe" sticker pack ($440).

This week Porsche released possibly the coolest accessory ever to be fitted to a performance car.

For an extra $4790, buyers of the new $250,000 Porsche 911 can have a "push to pass" button on the steering wheel.

Just like in Formula One, the driver can push the "response" button (the official name given by Porsche) which boosts the turbochargers to maximum power and selects the best gear for instant acceleration.

The power boost lasts 20 seconds, before the car returns to normal.

By way of comparison, the dearest options on the latest Holden Commodore include a "racing stripe" sticker pack ($440) and a coloured engine cover for V8 models ($350).

Meanwhile the dearest factory-fitted accessory on the new Toyota HiLux ute is leather seats, for $2000.

In the Ferrari catalogue, $2000 would only be enough to buy an embroidered prancing horse on the seat headrests, according to the price guide.

What's the biggest options box you've ticked? Let us know in the comments below.