Answer:
Because helium is a gas, it is not measured in weight, but rather in volume.
The 2009 retail price of a helium cylinder with 15 cubic feet of helium was about 30 Euros ($40 USD). This figure would represent $0.53 per gram of helium in the tank. Larger volumes have an estimated cost of less than $0.05 (5 cents) per gram of helium.