Look at the quoted cost of the new French carrier, more than double the cost of the QECs and just for one ship! It's not the cost of the cats and traps that are pushing the price up, at least not on their own. The supporting infrastructure has to be factored in, nuclear propulsion can't be just bought 'off the shelf', there are a lot of associated costs that go with it. The USN can spread those costs over a large number of ships, the French Navy has to concentrate it in one place and won't benefit from the USA's economies of scale.
All of this is not for the PANG - Porte-Avion Next Generation. The previous K-15 reactors have been used for the Charle de Gaulle, the triomphant submarine class and will be used for the next gen Suffren class.. some have also been installed in land for testing and developpement of the branch. --> Do not think that K22 is brand new. K22 is just an evolution of K15, meant to increase the power but limiting to the maximum the increase in volume, and it's meant to be deployed on the futur submarines too. So no, thanks to the PANG and futur vessels we're actually gonna see an increase in economy of scale in the acquisition, maintenance and developpment of the nuclear program (You could even say that, as France is one of the biggest user of nuclear power for civilian application, the benefits are even bigger).
What's driving the cost of the PANG ? Maybe the EMALS and AARG they're gonna have to buy from General Atomics. Maybe the increase in tonnage, the addition of brand new expensive equipment (like SEAFIRE), large automatisation (it will be much bigger, complex and "heavier" than the CDG yet will carry less crewmen...That's automatisation, and it's extremely costly) etc. The use of nuclear reactors might be signifiant but definitely not the only reason there's only one carrier.
In fact all you want is not repeat what's happening with the british Queen Elizabeth carriers.. that's cool they have two carriers but the budgets cuts made it so that they had to put one nearly out of service, and now it' actually sinking and won't be usable for 6 months. And they can't even buy all the aircrafts and equipment needed to fullfil the operationnal requierements for a single hull.. So they paid for the acquisition of two carriers, will have to pay the maintenance price for the next 40 years of 1.5 carriers, but in the end only have the equivalent at see of 0.5 carrier.