Also keep in mind, a lot of the cost of Hinkley Point is not so much the cost to build the reactors, but the financing. Speaking from memory, we are talking about borrowing at something like 10% over 35 years.
If France finances these new power plants, financing cost goes virtually to zero. So even if actually building the new reactors cost the same (unlikely, I hope they learnt a thing or two over the last 10 years...) they will end up a lot cheaper than Hinkley Point.