Enter your fireplace's wattage setting and daily use to see real running cost.
The flame-effect light alone typically draws under 50W — nearly all of an electric fireplace's cost comes from the heater element, not the visual effect.
Most electric fireplaces are resistive heaters, functionally similar to a space heater dressed up with a flame-effect light, and the flame effect itself uses very little power on its own. Running the heat setting for supplemental warmth in one room can still be cheaper than raising the whole-house thermostat, depending on your heating system's efficiency.
Yes — nearly all electric fireplaces let you run the visual flame effect independently of the heater, at a tiny fraction of the cost since the LED or light bulb draws very little power.
For heating just one room while the rest of the house stays cooler, yes it can be cheaper — but heating an entire home with electric fireplaces instead of central heat is typically more expensive overall.