Wow, that's a lot of money. I must admit i don't know about commercial fiber deployment so these numbers blow my mind. But from what i saw for the costs in big french cities (where there are established underground networks to pass cables) and french countryside (where you just use a tractor to dig "for free" on the border of a peasant's field) that sounds very expensive.

To my knowledge, all french highways and major railways are also already populated with fiber so you can just rent some point-to-point transit there from established operators without having to lay your own.

Good luck with this project keep us updated