hmmm about £40,000 new with the usual options, expensive but not for a race car that you can use on the road. I was going to say theres not much faster round a track, but not if the track is 1/4 mile long and straight, or an oval. I guess it all depends on the roads and driving style, I'm not aware of a US car which is useable on typical UK roads, let alone competitive or fun on a B road.
My point was that someone looking at an mx5 isnt really interested in straight line speed or ultimate grip levels, its the more tactile stuff which will entertain at lower speeds. given similar design and quality, something weighing 2 tonnes wont ever corner, brake or communicate as well as a car weighing 1 tonne.