Essentially to work out the price you look at the battery capacity say 64kWh & multiply that by your unit rate say 14.59p per kWh or as Intranicity says if you have Economy 7 or Octopus energy’s tariff 5p overnight.
It’s not an exact price as the batteries are always larger than stated & there are also inefficiencies such as heat generated but it’s close enough.
If you can’t have a 7kW charger a lot of cars come with or you can buy a 3pin household plug charger (often called a granny charger) they’re really really slow as rate limited so it doesn’t burn your house down but it’s enough to get you out of a hole if necessary.
There quite a few very very affordable EVs on the scheme from the MG ZS, Nissan Leaf & Vauxhall e-corsa available with no payment up front to amazing cars like the Kona Premium for £499 there’s even an 8 seater Vivaro elife for £1249 too with even more exciting cars due out this year like the Kia EV6 & Hyundai Ioniq 5 who knows if they’ll hit the scheme though.
Anyway lots of choice for very very little money. If you have a drive motability will fit a free 7kW charger for you subject to certain criteria or again the BP pulse sub, just check what the charger situation is near you if you’re relying on that.
Zapmap app will show you all the chargers their pruce, reviews & speed they can go & if your car has satnav most will find the nearest charger for you.
I’m ordering mine this afternoon I’m relishing the prospect of getting out more because I’m not sitting worrying about if I can afford diesel or not (pickup son from school is 20 mile round trip for example) going eV is going to be life changing for me.
Good luck with whatever you decide to do. I highly recommend checking the Kona out.