I recently experienced a similar situation during the Belgian Train Strike a few weeks ago.
Traveling with my family expecting to take the train from Paris to Ghent. All trains canceled. No cars in Paris or near by according to all the majors at the rental car desks I spoke with. I have top tier status with most of them due to my US Travel. Avis had an Audi a5 for 500 Euros for the day to pick up at airport and drop off in Brussels. - Can you say price gauge ? Strangely when I compared prices on the US vs French vs Belgium sites I found very different pricing and availability for towns in Northern France and Southern Belgium. I ended up book a car on the US Enterprise site for 75% of the cost vs the European sites.