You can buy a off the shelf kit to convert a Beetle to electric in the US has been about for some time.
Hear you go https://www.ebay.co.uk/itm/Electric-Vehicle-Conversion-Kit-for-VW-Frame-/200369951280 http://www.zelectricmotors.com/
I keep looking at this kind of kit...then run away screaming when I see the co$t of the batteries...!! I say a kit recently...about £3000 for the motor & all the control & charging gubbins, plus £10000 for the battery!!!! (as an example: Tesla Model S Lithium Ion Battery 18650 EV Module - 22.8 Volt, 5.3 kWh = £1,214 This was for something small/light like a kit car/Fiat500/VWBug. The motor developed 47bhp... I think I calculated that I'd need to use the car for 25years to recoup the petrol money saved (and this assumed free electricity!!) Look at it this way...the cost of an Engine, between petrol or electric is probably comparable(ish), however the cost of the fuel tank certainly isn't!!! I found a kit aimed at a VW Karman Ghia, that used as 650A 95v motor - this suggests it uses (and I'm no expert here!!) 62kw/hr (lets assume we're on the motorway and have a heavy right foot!!). lets assume a for the stock KG, 45lt tank & 3.3lt/mile = about 150 miles/tank, so lets say 3 hrs driving/tank. Petrol costs about £1.30 per ltr, so 1 tank costs about £60/tank. Electricity cost (on average in the UK) 13p/kWh, so 62kWh x 3hrs = £24 So...assuming you pay average UK prices for the electricity or petrol, you will save about %60 on fuel costs...that's about 278 tanks to break even, or 42000 miles...probably not unreasonable for your daily driver....money back in 4 years...but a but of a leap for your average Classic...
There's a guy on youtube with a samba that's all electric his house has a home made telsa power wall. Well done it is too
I know I've just bought a type 4 to go in the project but I still keep coming back to this electric option ... and I think if you can use your classic as a daily runner then, as you say, it "pays" ..... Having trouble letting go of the "iconic sound" though