From the central station I guess it should run around Euro 30, however I would recommend to take the Metro to Louise, where you have to change to the Tram anyway, a taxi from there should run around Euro 5-8, basicly only down Avenue Louise for a mile or so !

If you want to take a taxi from central station you would have to schlepp your luggage all the way out to the taxistands, when you take the Metro the way is shorter and the Metro trains are huge, hardly comparable with those small trains in London for example, same is true for the capacity levels, not nearly as full as in Paris or London.