I've tried to assess 'real world' costs by using the amount of home charger power required to bring the %SoC back up to 80% after driving the car for approx 65miles. I then calculated the 'real' miles/kWh and divided by the car's indication of miles/kWh: approx 2.6/3.3 ~ 80%
At 7p/kWh & even allowing for standing charge, this is about 2.8p/mile.
With this kind of efficiency level, using a public charger may increase the 'ticket price' by 25%
Don't get too hung up on my figures because there will be rounding errors associated with 80% SoC cut off, Hypervolt charger estimate of charge, car's calc for m/kWh, & so on.
My maths and/or assumptions could also be iffy, & results are probably influenced by temperature. But its a start.