According to a report from an interdisciplinary panel from MIT (PDF), the United States could create the capacity for 100,000 MWe of enhanced geothermal in just 50 years with relatively modest investments.
The estimate of what it could cost to ramp up the enhanced geothermal infrastructure is $800 million to $1 billion over a fifteen-year period. Solar and wind are intermittent power sources, though storage systems may make them more attractive over time. Geothermal plants, once established, tend to produce energy nearly constantly and can even outperform coal plants.