Building a pyramid, in the ideal case, simply requires the energy to lift each stone into place. Lifting 6.5 million tons of stone on average 40 meters (remember that most of the weight of a pyramid is at the bottom!) uses 6.5e9 * 40 * 10 Joules of energy, which is 722 MWh, which costs $144,000 in (California) electricity. Okay - thats a lot more than I expected actually...