"Competition is Good!"
Levelized Cost of Energy from Fossil and Renewable Sources (2016)
The "Levelized Cost of Energy" (LCOE) is an apples-to-apples comparison of the cost of new electricity generation from different sources. It's the all-in lifetime cost of power generation from a facility divided by the total amount of energy produced during the facility's lifetime. These numbers are in $/MWh (dollars per megawatt-hour), although many people are more familiar with ¢/kWh (cents per kilowatt-hour) which equals the numbers in the figure divided by 10. These are wholesale generation costs, but for reference, the average residential retail rate for electricity in Colorado is about 11¢/kWh (or $110/MWh).
The cheapest source of new electricity is wind (3.2 - 6.2¢/kWh), followed by utility-scale solar (4.6 - 6.1¢/kWh). For so-called "baseload" power, natural gas (4.8 - 7.8¢/kWh) beats coal (6.0 - 14.3¢/kWh), which is why the cheaper fracked gas is driving coal and nuclear out of the market (in states where there is competition). Vertically-integrated monopolies get to protect their old coal generation. Even in states with RTOs and competitive wholesale markets, there are "around-market" moves to protect expensive nuclear assets by assigning a value to their low-carbon electricity to make nuclear more competitive with gas and renewables.
An important threshold was recently crossed: gas-peaker plants, which ramp up to serve the late-afternoon peak demand period, cost 16.5 - 21.7¢/kWh. This can already be beaten by "dispatchable solar" (solar + battery storage) that can "time-shift" cheap and abundant midday solar generation to serve the same peak demand much cheaper. On the Hawaiian island of Kauai, solar+storage was contracted at 14.5¢/kWh in 2015 and then at 11¢/kWh less than a year later, because both solar and batteries are rapidly coming down in cost. So, in a free electricity market, new gas peakers can no longer compete in many locations.
It's important to note that the cost of solar and wind will continue to decline (see "Disruptive Technologies"), whereas the cost of electricity from fuel-based sources is likely to remain the same or increase over time. If we are planning for the future, our electricity system should be able to take advantage of these trends.