I've watched the Vintage Voltage series from the start. It intrerested me initally...but the cost of the conversions they do are seriously high. Trying to fit great lumps of batteries into a car that never meant to have them is never going to be simple...and the battery boxes need to be robust.
The Enfield episode......yeah...I am sure the guy is happy with his 20K Indian Enfield. I read somewhere it weas capable of about 70mph top speed, with a range of about 80 miles. According to the article I saw, the commission to build it actually came from Enfield themselves, though the show dressed it up as some guy wanting a nice quiet bike to commute on.
A Zero FXE .... nice little town bike...max speed 80mph and a range of 100 miles of city use...£12,300
If you are going to spend something like 20K ...you can get a top of the range Zero. Still not 'fast' ..... but able to exceed the speed limit in the UK, and do it for a couple of hundred miles.
I am sure there are cheaper DIY conversions.....and I don;t mean the frankenstein horrors you can search up on YouTube!