Ha! I have been surfing and have found a few indicators of N`s piggy bank.
Pierre Branda: `Napoleon et l`argent. Le prix de la Gloire`, published by Papot, 2007.
But, much more interesting: `Collision of Empires`, by Arnold D Harvey, 1992. In which, on page 63 we read: `After Jena, Prussia, Saxony and the minor German principalities handed over 500 million francs`.
Later, same page: `La Bouillerie (Tresorier general du domaine extraordinaire) estimated the sum to be 470,467,387 francs. Daru (Intendant general de la Grande Armee) said it was 513,744,410 francs`.
Either way, I suppose that it was a vast sum in those days.
Also on page 63: N wrote in 1807: `A soon as my army has entered Portugal, it must be fed, clothed and paid by contributions which shall be levied in that country; from that moment on there must be no need for me to send another half-penny.`
What a guy!! My admiration for him grows by the hour.