OK. If you are serious, then head up the motorway to Mulhouse and the Wittenheim trading estate. There's a shop there that sells cheap arty stuff. Canvases are a fraction the cost of ones in CH.

Unfortunately I can't remember the name, but it is almost directly opposite on the other side of the dual carriageway from the Decathlon (Rue des Mines Anna, 68270 Wittenheim, France).

PM me if you want more details.