MM was renowned for their attention to detail with even the props, so I doubt it was as cheap as one might think, Breaking Bad had some impressive visuals (not effects, granted, and due largely to the scenery which was in a cheaper-to-shoot state), but Walking Dead can't be cheap, nor the spin-off, which has had some pretty big sets, in addition to the zombie effects. We're not talking zombies overrunning an isolated farmhouse here, but beaches, city riots, army bases.