From what I've seen of other small car conversions - 2CV van, Fiat 500 etc - I'd imagine we're talking around £20,000 plus the base car. Given the market values of Bugs these days anyway, I'd say that's not an unreasonable investment. And for a car like the Bug, where engine work is physically so restricted and inconvenient, but where the weight is so low that range between recharges is pretty sensible, it ticks a lot of boxes. I'm seriously thinking about this for the Webster if I ever get time to do any more work on it!
I presume that with the acceleration of an EV, it might make sense to get one of Joe Mason's disc brake conversions too, especially on the front wheels.