Here's a somewhat unusual arrangement offered by Air France who will fly you to Paris Charles de Gaulle airport and then whisk you downtown Brussels in little over an hour by high-speed train to the Midi-Zuid railway station.
With its built-in airport transfer and check-in time, this itinerary compares favorably to a non-stop flight in total travel time. The savings are only about $35 plus the price of that Brussels airport transfer you won't need, but as a bonus you get to see France whiz by at the speed of a very fast locomotive.
Along with other fares we have posted to Brussels, this one is currently available for $475 from both Newark and New York JFK for travel starting late October. You may be able to get it from other Air France gateways or find code-share connections from many other cities, but before you rush off to this storied land of beer and chocolate and fries do as your mother told you and finish your sprouts!