If I found out my government blew 20k to slobber on Musk's balls instead of using that money to create work for our own people, I'd personally go blow up that antenna.
And you said it yourself: Starlink already exists. They don't need a subsidy. You bring the cost of Starlink down by forcing them to compete on the merits of their own service, not by throwing money at them.
The cost is the contractor's hours to get up a ladder on each electricity pole from the closest PON splitter to the customer's home, plus the fiber itself which is peanuts at volume.
Everything else (permits, pole rent, etc) is accounting money that can be negotiated. If there's a strategic national program to fiber up the whole country, this could be exempted on a pen's stroke, or depreciated in many decades.
The local fiber guy goes out of business... you still have the fiber line there.
Its investment, not subscription.
$0. It's taxpayers euros.
But it's not inefficient if this fixes a chicken-egg problem: overcrowded big city and underpopulated rural area sucks.
Nobody can/wants to go in rural area if they can't make a living there. A fiber speed Internet unlocks lifestyle for many.
It's the same as investing in say a high speed railway between major cities A and B and adding a middle-of-nowhere stop C midway. That C then can flourish to become a medium/major city... So while the initial investment looked like a waste, it's beneficial to provide a better life for people living in both A,B, and C.
I don't know how it works in France, but in many European countries phone/DSL lines and fiber is highly regulated. Even if it is run by a company, they usually have to provide fair access to other providers so that there is competition. For instance, we have a XGS-PON connection to home (used to be AON) and I can probably choose at least from ten ISPs. This is nice, because they try to compete on prices and bandwidth (e.g. the company that owns the network we are on offers 4Gbit symmetric max, but a competitor offers 8Gbit over the same fiber).
Much harder to accomplish that with satellite internet and foreign companies.
Also ignoring the political implications of a country spending tax money to buy services from a highly political company from a country whose politics and world influence are in flux right now.
Starlink is good because it is easy to deploy quickly. But the entire constellation and service will be dead within 5 years without constant launches of new satellites.
Forget efficiency. That sounds like a very poor investment of tax dollars to me. The fiber laid will provide lower latency and higher bandwidth connections for the next 40 years.
Not everything has to be a capitalist 'minimize cost, maximize profits' game.