Personally I don't understand how a Leica APO-Telyt-R 1:5.6/1600mm would be worth 2.79 million dollars. Thats really in WTF territory for me. Unless all the glass is sapphire crystal or something ridiculous.
The thing that makes it so expensive is that this is a one-off custom built lens (as you could read in the linked article). All the development costs will be included in that price.
5D3, 16-35 L, 24-70 2.8 L II, 24-105 L, 85 L II, 70-200 2.8 L IS II, 135 L, 100-400 L, 50 1.4, 40 2.8, Sigma 180 3.5 EX macro, 1.4x TC III, Speedlite 600EX & 550EX