A home 3D printer (like an Ender 3 or Bambu Lab) consumes an average of 100W to 300W during operation, depending on the bed and extruder temperatures. This is roughly equivalent to a desktop computer's consumption. To calculate the exact cost on your bill, you need to multiply this consumption by your local kWh rate.
To calculate the exact electricity consumption of your 3D printer, multiply the machine's power (in watts, W) by the print time (in hours) and divide by 1000 to get kilowatt-hours (kWh). For example, a 200W printer running for 5 hours consumes 200 × 5 / 1000 = 1 kWh. Then multiply those kWh by your local electricity rate. A more accurate method is to use a smart power meter (wattmeter) plugged between the outlet and the printer to measure real consumption, since power varies throughout the process depending on bed heating, hotend, and fan speeds.