We've got one night there and are comfortable spending up to $50 per person (all-inclusive) for dinner. Any suggestions for local (Belgian) cuisine in that price range on or near the main square?
Its a little touristy on Restaurant Row, but can't beat the Moules Frites at Chez Leon.
Depends what you mean by "all inclusive". A bottle of wine can push your bill over that even in moderately-priced restaurants.
Most of the restaurants around the "main square" are either top end or very overpriced and poor quality tourist traps. I'd look into walking a way or even taking the tram/subway. Try the Marolles or Saint-Catherine/Saint-Gery districts.
We ate at this restaurant in October--it isn't fancy but it's good food in a fun atmosphere--it's not far from the Grand Place. Here's the website with the address--the website is in French:
La Fin de Siecle Restaurant
Most Belgian restaurants offer a selection of "menus" (European definition of the term, meaning an apetizer, one or two courses and a desert) for dinner, usually minus the drink. Any restaurant on Rue Boucher should offer you a menu for less than $50, although I can't guarantee you that the food will be that great. Leaving the rest of the tourists behind, go a little further afield to the large square by Eglise St. Catherine and you'll find some pretty good seafood restaurants. In the Upper Town, also not too far from the Grand Place, there's another good cluster of restaurants and cafes around Place du Grand Sablon.
Two places I can heartily recommend. While on the Grand Place, 't Kelderke (yes, the spelling is correct) is not a tourist trap. We learned about it from Frommer's - http://www.frommers.com/destinations/brussels/D47121.html Get there early or late, because it fills up quickly. FYI, the entrance is on the lower level. It took us a few minutes to find the door!
While it's not Belgian cuisine, there is a great Italian restaurant just south of the Grand Place,
La Boule Rouge
Rue des Pierres, No 52
phone 02 511 94 00
And they have very good gelato.
"'t Kelderke (yes, the spelling is correct)" In case anyone was wondering (I know you all were!), "'t" in Dutch is a contraction of "het", meaning "the".