I know this is old news, but a reader pointed out to me (thanks Andreas) that the Leica APO-TELYT-R 1:5.6/1600mm may not be the most expensive lens in the world. Take a look at this monster – Zeiss Apo Sonnar T 4/1700mm:
The “tiny” black cube at the end of the lens is a Hasselblad camera.
I could not find any info on the price, but this is definitely the largest telephoto lens in the world (beats Leica by 100mm)...