Question : Interested in traveling in the next 30 days and want to get the lowest fare?
Answer : Since low prices are preferred, look at Mar 26th. As of Feb 27th, it's showing the cheapest ticket sales at $703. That is 4% below the average price for this route, so you can spend that extra cash on an adventure rather than the flight.
Question : Is the price you found a good deal?
Answer : Ranging from $703 to $770, prices for IAD to LIL fluctuate a lot less than most routes from the United States. However, the sooner you book, the more you'll be able to save.
Question : What is the cheapest round-trip ticket you can get to Lille?
Answer : Air France is offering the best deal at $703. Better snatch it up quickly because prices range all the way up to $770 over the next three months.
Question : How long do most people visit Lille?
Answer : Of course you're not most people, but if you were, you'd stay roughly eight days.
Question : Would you be willing to change your travel days if it saved you money?
Answer : In March, Sunday is your cheapest day to fly. Flexibility is paramount when booking travel plans in order to keep travel costs down.