trois fois rien

almost nothing at all

This expression means a tiny, insignificant amount, practically nothing.

J'ai trouvé cette veste au marché aux puces pour trois fois rien.

I found this jacket at the flea market for next to nothing.

The humorous logic is that three times nothing is still nothing, but the multiplication emphasizes just how little something is. Recorded since at least 1838. Interestingly, the French word 'rien' originally meant 'something' (from Latin 'rem'), so there is an old layer of irony baked in.