What’s your current electricity a day?
if you estimate 3 miles a kWh you’d need between 5 and 7 a day for your car.
on intelligent octopus go that’s a max of about 52p (7.5p)
If they give you a charging schedule during the day you’ll also get cheap elec for your other use, so showers, washing etc will be cheaper then too.
do the sums for your current tariff and your potential, but I’d hazard a guess you will be cheaper shifting