Since you are already using insulin, please learn to hometest the blood glucose asap to keep him safe. You'll need an inexpensive human glucometer, such as the WalMart ReliOn Confirm or Confirm Micro, matching test strips, and lancets for alternate site testing (26-28 gauge)
Another insulin is ProZinc, which runs roughly $120 per 10ml vial which contains 400 units. It has 40 units per milliliter (mL), so it is a U-40 insulin. It works similarly to N, but lasts closer to 12 hours.
Compare insulin costs on a per unit basis, not volume.
If you get Lantus, get the pens *5 * 3 mL), not the vial (10 mL). This will let you use most of the insulin without waste. You will use a syringe, not the pen needles, to get the insulin out of the pen. Lantus has 100 units per mL, so it is a u-100 insulin.