Your kitchen uses 450 watts of lighting. How much does it cost if the lights are on for 8 hours a day, every day for a year if the local electric company charges 9 cents per kWh?
Most of the time, people use foam cannons to wash their vehicle with their pressure washer because a pressurized washer can knock dirt off better than a standard garden hose. However, if you enjoy having a car that is even cleaner than what a pressure washer can do, then you need a foam cannon.
The key thing to using the foam is to get the foam to water ratio right, so that the foam sits on the car for long enough. trust me, I have used both and the snow foam guns (that dont attach to a pressure washer) are not a patch on the lances that do attach to the pressure washers.