Which cost less to operate 120 v appliance or 220 v appliance?

For the most part, they cost about the same. For instance, if you look up a 120V, 2hp electric motor in a catalog, you will find it draws about 18A. 120V * 18A = 2160 watts. If you look up a 240V, 2hp motor, it will draw about 9A. 240V * 9A = 2160 watts. Watts are watts. Watts are what you pay for. It takes a certain amount of power to perform a particular task, irregardless of the voltage supply. You typically see larger loads, such as a dryer, range or AC unit fed from 240V. This is because the lower current draw permits you to run smaller wire, which is less expensive to install.