It's a fast and costly toy indeed, but that's the way it is for the extreme segment of cars with combustion-based engine too. Look at Bugatti Veyron - "the fastest street-legal production car in the world" weighting almost two tons! That's OK for Rimac to be heavy. Also, the safety requirements are not so strict if the car is manufactured only in a limited number (and looking at the price-tag, it's safe to say that limited production quantity it will be).