I agree with ContinentalOp, and do about the same. You are firing more defensive ammo than that, so IMO you are doing even more than necessary. When you use defensive ammo rather than target ammo, do you feel a difference in your hand or see a difference at the target? This may affect your decision (if there's no difference in practice, there is less need to practice with defensive ammo).

I'm sure you already shop around, and stock up when it's cheap. This has gotten me through a few ammo shortages, also.