There are 6.6 billion humans on the earth. If the average human weighs 150 lbs (likely to be an overestimation, as many humans are children), the total mass of all humans is 1 trillion lbs. There are about 1 billion sheep, which weigh roughly the same as humans, for a total sheep weight of 150 billion lbs. There are about 1 billion pigs, which weigh around 250 lbs as adults, for a total pig weight of at most 250 billion lbs.
If purchased directly from the Bureau of Land Management, helium costs $60 per thousand cubic feet this year. A thousand cubic feet of helium lifts 28.2 kilograms or 62 pounds, so the cost to lift one pound with helium is about $1. Lifting all humans, pigs, and sheep would then cost $1.4 trillion, which is less than Joseph Stiglitz and Linda Bilmes' estimate of over $3 trillion for the cost of the Iraq War.
Image adapted under a Creative Commons License from Sam the Sham.