I just read an article on the BBC website about a few companies in London that converts classic cars (or any car you take to them I guess) from petrol engines to electric.
The very cool part is that they mostly use 'recycled' parts from electric cars, like Teslas and Nissan Leafs that have crashed and would otherwise just be thrown away. The environmental footprint of converting an existing car to run on an electric drivetrain is much much lower than it would be to build a new electric car, and if the parts are basically being reused then it's even better.
The price is huge at the moment, with one of the companies charging about £20,000, but they say they are working on cutting it down to around £5,000 which makes it much more affordable for most people. If this became a bigger industry/trend, with more companies doing the same thing, then the price would definitely come down, just as it does with any mass adopted tech.
BBC article: https://www.bbc.com/news/business-58578061