There’s pretty much no way a $100,000 car can be more environmentally friendly than a $20,000 car. This is true irrespective of the way in which the cars are powered. If you buy a $100,000 car, you put $100,000 into the economy. That is, $100,000 becomes available to the manufacturer’s suppliers and employees to buy stuff, and there’s no reason that this money will be spent in a more environmentally friendly way than any other $100,000 that goes into the economy.
I think the only way to make the purchase of a $100,000 car environmentally friendly is to buy a $20,000 car, and burn $80,000. At least that way you get rid of $80,000 that would otherwise be used to consume stuff.
(If an electric car ends up being cheaper over its lifetime (i.e. including fuel/power) then it will be more environmentally friendly than its gas-powered equivalent. But I don’t think this would ever apply to the Tesla Roadster.)