As of my last knowledge update in September 2021, the world’s most expensive cars are often limited edition or custom-built supercars and hypercars, crafted with high-quality materials and cutting-edge technology. Please note that prices and availability may have changed since then, but here are some of the most expensive cars known at that time:

1. Bugatti La Voiture Noire: Priced at approximately $18.68 million, the Bugatti La Voiture Noire is a one-off hypercar inspired by the classic Bugatti Type 57 SC Atlantic. It features a powerful quad-turbocharged W16 engine and exquisite design.
2. Pagani Zonda HP Barchetta: With an estimated price of around $17.5 million, the Pagani Zonda HP Barchetta is a unique hypercar with a powerful V12 engine and an open-top design.
3. Bugatti Centodieci: Priced at approximately $9 million, the Bugatti Centodieci pays homage to the iconic Bugatti EB110 and features a potent quad-turbocharged W16 engine.
4. Bugatti Chiron Super Sport 300+: Valued at around $5.74 million, the Bugatti Chiron Super Sport 300+ is a limited edition version of the Chiron, designed to surpass the 300 mph mark.
5. Lamborghini Veneno: Priced at approximately $4.5 million, the Lamborghini Veneno is an extremely limited edition hypercar with a V12 engine and a striking design.
6. Koenigsegg Jesko: Valued at around $3 million, the Koenigsegg Jesko is a high-performance hypercar with a twin-turbo V8 engine and advanced aerodynamics.
7. Mercedes-Maybach Exelero: Priced at approximately $8 million (sold for $8 million in a private sale), the Mercedes-Maybach Exelero is a unique and luxurious coupe with a powerful V12 engine.
8. Pininfarina Battista: Valued at around $2.5 million, the Pininfarina Battista is an all-electric hypercar with stunning design and impressive performance.
9. Ferrari LaFerrari Aperta: Priced at approximately $2.2 million, the Ferrari LaFerrari Aperta is an open-top hybrid hypercar, combining a V12 engine with an electric motor.
10. McLaren Speedtail: Valued at around $2 million, the McLaren Speedtail is a limited production hyper-GT car with a central driving position and a top speed of 250 mph.

Keep in mind that these prices are approximate and may vary depending on factors like customizations and local taxes. Additionally, new hypercars may have been released or existing models may have appreciated in value since my last update.