A British man posted a video on his YouTube Page showing off his multi-rotor manned flying machine called "The Swarm". Using 54 counter-rotating propellers, the flying machine can fly for up to ten minutes using its four cell batteries. The props are standard RC aircraft 18-inch propellers and weigh less than 1KG each. Up to 6 more can be added in the middle without a pilot that would likely allow it much more lift. Gasturbine101 says he never intended to make a significant journey or to fly much above head height and simply just did it for fun. He also says the approximate cost to build it was £6000 or roughly $9200 USD.
The Swarm man carrying multi-rotor airborne flight testing montage. 54 counter-rotation propellers, six grouped control channels with KK2.15 stabilization. Take off weight 148kg, max lift, approx. 164kg. Endurance10 minutes. Power approx. 22KW.
Props at 18 in were the largest I could find with contra rotating pitches and so defines much of the layout. Also the fine pitch allows them to turn at high speed which reduces motor weight for a given power. Motor KV chosen to work with 4 cell batteries with 20% or so control margin. This low margin maximises the ESC efficiency, higher margin results in higher circulating current losses in the ESC and motor, reducing endurance.