I think the fault is all on John's side. At one point, I belive when they have to give up the idea of making it to the castle, John blames it on James's horse saying James should have a horse and gig of his own. Catherine literally tells him that James can't afford it. When John asks why and she says that he doesn't have the money, John refuses to believe it. He still prefers to believe that the Tilney's are rolling in money and that James is just being miserly.