I've just been looking into getting a used one of these. You can pick them up for £6k, and either leased battery for £70 per month or pay a bit more (£5k on the new price) to own it.
The electricity appears to be free if you sign up for polar plus for six months, then £7.85 per month afterwards. Seems nice and cheap.
On long journeys you can stop at most service stations and top up, with it taking 30 minutes to do at least 80% of the battery. Since we always need to feed the kids on long journeys, that's no really problem.
I can't charge at home, so i would be reliant on charging at the Waitrose at the school run, which could do 30 to 60 minutes per day. That would keep it mostly charged up. There are other charge points within a five minute walk of home, one is a 7kw one as well.
I might get one of these. What is the downside?