This depends on how much water you use in your home, and therefore how often the pump needs to come on to pump out the excess water.
In a normal household, with 2 Adults, 2 Children, we say that it costs the same as a refrigerator to run. Remember, we have an aerator running 24 hours a day, and the pump turns itself on when the water reaches a certain level. So, the more water which gets used, the more electricity needed to pump out the water.
Very economical indeed!