Simply not true, the lines held until AFTER the armistice. It was also shown the bigger forts could have withstand an atomic blast, those were amazing examples of architecture.
The problem, as far as I remember, was that building a line of forts alongside the Belgium frontier would have been interpreted as a belligerant move by the Belgians. The Belgians then said they would build a line of forts in case but were too trusting in their neutrality and botched the job.
Concerning the price, the Maginot line was only a tiny part of the French military budget, the problem was political and diplomatic
EDIT: I found a figure, Maginot line was (supposedly) 5.5% of French military budget every year of its construction. So, an effort yes, but nothing that bad it will bleed out the militaries.