Not a massive hurdle. BMW got the i3 to be street legal in the US without much trouble. And I know, the i3 was only a smaller car, it wasn't a cheap car (I think they went for around $40k new)... but that's just BWM.

Getting Renault e-Twingo / Citroen e-C3 street legal in the US wouldn't really rise the production cost much. But nobody is going through all the trouble, because (obviously) almost no American would buy such a car, even though they start at <$20k new.