I don't see why they need to be more expensive than they are - it helps to own one of them in order to beat them in the hardest two rally events, and they're already twice the price of the Toyota GT-One road car which is head and shoulders faster than anything else when tuned, with similar power to the Escudo PP and only 100kg more weight.
Also, why should they be more expensive? The fastest car in the game is also the (joint) most expensive. That sounds fine to me. Why should they be harder to get? To force some artificial extra difficulty on players who don't necessarily want it, hence why they're buying the Escudo PP? Increasing the grind just makes the game less fun, it's not like anyone is forced to drive the Pikes Peak cars.
I realise that that point is to make it harder for players to acquire those cars, but it's just unnecessarily punitive. The average casual player will take quite a long time to afford them at 2m credits without looking up grind strategies, and if they were more expensive it'd just incentivise using the GT-One for everything instead. If the GT-One was more expensive, then the XJ220 can also exceed 950ps, and so on. Eventually you'd end up with average players struggling to get a car good enough to win the World Championship.