You only covered the bolus requirements.

You also need a basal insulin for Type-1 diabetes (unless you're on an insulin pump, which is an entirely different class of expense), so something like Tresiba ($505) (https://www.goodrx.com/tresiba) or Lantus ($357).

Still not $1300/mo, but your price is also using temporary rebates and coupons, which certainly aren't always available.