Historically natural gas is more expensive than coal per kWh(e). Natural gas plants are not very intrusive and cheaper than coal to build, so utilities throw up many of them but avoid running them unless they need them, e.g. peaking power.
As of 2006, least to most expensive, in the US
To Build, assumes no backup power ($ per kW):
Natural Gas Combustion Turbine $670
Natural Gas Combined Cycle $730
Wind $1750-2400
Coal $2080-2740
Solar Thermal $3150-5700
Nuclear $3500-7000, Biomass $3500
Solar PV $8100
To Operate and Maintain only, per unit energy generated (cents / kWh)
Solar Thermal (1), Wind (1.7 ), Solar PV (4.1) , Hydro
Nuclear (3-4 cents, 2015 est)
Coal ()
Natural Gas (2-3X coal)
Levelized Cost: Build and Operating costs combined (cents / kWh)
Coal 7.5
Gas Combined Cycle 8.6
Gas Turbine 17
Nuclear 13 in 2016
Edit: adding in actual O&M costs as I find them.
http://www.psc.state.fl.us/utilities/electricgas/RenewableEnergy/Full_Report_2008_11_24.pdf