Hve you checked the difference between gas and electric utility rates? The electric units will either have to have a very large amperage, requiring large wires and circuit breakers, or a low flow capacity to allow the heating to take place. If low capacity, you will not be satisfied, and if high amperage, your house wiring may not be adequate. Regardless of the water heater type, you still have to heat the water you use. The only benefit of a tankless one, if it is installed at the same location as the tank type, is that you do not have the small amount of heat loss. Otherwise all the factors are the same, and there may be little economic advantage to making the change.