Due to legislation passed in 1996, the United States reserves of helium must be sold off within the next five years, which has led to the lifting gas being criminally under-priced. According to Nobel laureate Robert Richardson:
The Earth is 4.7 billion years old and it has taken that long to accumulate our helium reserves, which we will dissipate in about 100 years. One generation does not have the right to determine availability for ever.
Unless we find another hidden reserve of the stuff, expect highly-flammable hydrogen balloons to replace helium once it runs out.