Quatre-vingts, quatre-vingt-un, quatre-vingt-deux... quatre-vingt mille, quatre-vingts millions. This doesn't affect pronounciation in general, because this s is silent... except in the context of liaisons, such that you would say "quatre-vingts (z')avions" and not "quatre-vingt (t')avions", although in colloquial speech, nobody cares. In written form, I expect many of my fellow French native speakers to do the mistake or at least be uncertain. We mostly write it "80" anyway.