Years ago i was looking for EV kits and found several people out there selling them. Idk what the current availability is, how much tech they have, or how open they are. The ones I saw were pretty low tech (lacking regen braking and such). Think accelerator pedal controls motor speed and a battery pack is about all they were. Again this was a while ago when I was looking (like 2010ish).

You could offer kits for older vehicles, but considering the cost of the kid and installation cost/effort, does it make sense to start with an older car that may have other issues coming soon?

So what's the alternative? Start with a new car and throw out the ICE? Sure, but a bit wasteful and even more expensive than an older car or you could find an existing manufacturer (idk like Lotus) who will basically provide you the car without the ICE related components (aka a glider). ;)