I consider myself moderately overweight at this point (maybe 10-15kg). If I lost weight, I could reduce the baseline amount of insulin I need every day, thus reducing the amount of insulin overall that I need to pay for.
I also fully acknowledge that, upon getting an insulin pump (16 years ago), I instantly became aware that I had much more freedom to eat what I want, when I wanted and thus, put little effort to cutting back on sugar outside of switching to diet drinks. If I were to switch to a low-carb diet, or no carb (which is admittedly very hard, I've tried), I could further reduce my insulin costs.
Personally (keep in mind these numbers depend highly on each individual), if I got my weight down 10kg, and ate < 100g of carbohydrates per day, I could theoretically only require ~35-40 units of insulin per day. At 40 units, I would only need ~1.35 vials of insulin per month. Ballparking, I'd say my current rate is likely around 2 vials per month.
I eat whatever I want (mostly pasta usually) and I need 20 units a day at most. (100 units/ml dosage).
It kinda sounds crazy, and I used to think it was, but I'm currently low carb to lose weight (lost 28 pounds in 3 months with it so far!). It just takes a couple weeks of training while on the diet to get your body to catch on and be back to your usual performance.
There are actually a surprising number of world records set by athletes on low carb diets who destroyed previous records that claim their diet is the main reason they were able to accomplish their goals
Source: The Art and Science of Low Carbohydrate Performance by Phinney and Volek