We were thinking about this.

We’re looking for used LARGE military or weather balloons. Preferably a lot of them. The best we’ve found were some new (and expensive) Chloroprene/latex weather balloons and we’d have to buy 15 of them at their max volumes. We also found some 24 year old Kaysam balloons on ebay that have a lifting capacity of 118kg per so we’d only need about 3-4 of those…

— Ryan Davis