20 kilos on the spring balance, with the weight of the eight speed-controllers added. At 44 pounds that's around half of my original estimate for the mass of a competition airframe.
With jet-packs and parameters weighing in anywhere between 25 and 30 kilos that leaves us around a further fifty percent or 10 kilos to dedicate to battery-packs.
My guess is that isn't going to get us far, but getting us safely airborne represents first base.
Build it and they will come.