Besides often being broke, Vincent had a strong compulsion in his final years to complete a painting every day. Sometimes he was forced to reuse canvas then. (Part of his final style too to get the paint on as fast as possible with large strokes.)
Some of Van Gogh's paintings are so thick, that underneath an outer layer of dried paint, there's still liquid paint trapped underneath, which may not dry for another hundred years.
But yeah, he was known for re-using canvases, as were many impressionist and post-impressionist school painters.