For a 35-lb tumbler the gas consumption per load is 34,853 BTUs which is $0.383 per load (assumes average cost of natural gas at $1.10 per therm). Energy to run the motors and control is approximately $0.025 per load (assumes $0.065 per kWh of electricity).
Therefore, the total cost per load is approximately $0.41 per load.
The answer to this question can get a little tricky since variables come into play beyond our control, such as wetness of the load, size of the load and time set on the control.