May I present to you the $50 option: AMG Door Pins on the CLA45AMG

I especially love the description:

Create added space for sports equipment and luggage with one of our aerodynamic roof containers. Constructed of light yet durable thermoplastic, each container features a security lock and opens from either side via gas struts, for easy loading. Three sizes are available: 16 cu ft and 14 cu ft, available in black metallic or matte silver, or 11.5 cu ft, in titanium metallic. Each has a maximum load capacity of 110 lbs, and requires the roof rack basic carrier (sold separately).

Wait a minute, they didn’t even add the right description...