How much (pounds) are you feeding? What were you feeding before when he was in good weight?
I don't know if I would increase the alfalfa pellets as they can be a choking hazard as can the cubes.
Since the price is comparable, why not feed more of the chaff, or add fat to the diet? Are you feeding any concentrates?
I think I understand what you're getting at-you don't want to pay for "moisture", and I totally agree with that, but the pellets would more than likely have some moisture content as well, and won't supply the long-stem forage desirable for digestion.