In Western economies, more energy is used to operate buildings than to operate transportation  Much of the decline in energy consumption since the oil crisis of 1973 is due to more efficient use of energy in homes and offices  New building technologies, which make lighting, heating, and ventilation systems more efficient, have cut billions of dollars from energy bills in the West
Since energy savings from these efficiencies save several billion dollars per year today, we can conclude that 50 to 100 years from now they will save more than $200 billion per year (calculated in current dollars)
Technology used to make buildings energy efficient will not become prohibitively expensive over the next century.