Cost metering was not the intent of the application. I use it to send a message when the power meter senses that a cycle of usage as ended.
It looks like someone has added a device type over in this thread Adding kwh cost to Aeon Labs Smart Switch, but it looks like it is a work in progress. The basic device reports energy in kilowatt-hours (kWh), so it should be simple math to figure out cost (assuming you do not have time-of-day pricing for electricity).