£0 if you put chargers in your workplace for everyone to use for free .
On a serious note if you don’t have free access I guess based on a 70kw car, at 25ppk it going to cost you the best part of £20 to fill up, I get 200 miles from a full charge. You can get tariffs where it’s cheaper to home charge, but I don’t have a home charger so other posters will be better placed to advise.
if I’m ever stuck (rare) I’ll pay the 85ppk at McDonalds, I find their superchargers reliable and quick.