Thanks so much for the input, advice and well wishes everyone!
I went and picked up the insulin and gave Taz his first shot tonight. He will be getting shots twice a day for now. I was advised to give him the meds for 3 or 4 days, and then check his blood sugar again about 3 hours after his shot. He took his shot like a total champ, and got a small piece of plain baked turkey breast (skinless) as a post injection treat.
I have warned my girls not to give Taz anything for now. Thankfully I was already in the habit of buying soft natural treats, and slicing them very small (in Tia's agility they get a LOT of treats, but I didn't want her to gain weight, so I every 4 or 5 agility treats actually works out to 1 normal sized training treat lol), so their impact on Taz should be very small. We need to weigh out the pros and cons here. He is basically at "end of life" age for a Rotty, we knew that when we adopted him, but we want it to be a GOOD end of life. We want a happy dog that can feel as though he gets treats sometimes too. That is why I bought the skinless turkey breast, so I could cut it into small pieces and give it to him as a 'post injection treat'. With it being straight protein, and small pieces they shouldn't have too big of an impact on his blood sugar.
Turns out this is going to be fairly expensive though. If he does well on the dose he is on right now (25 units, twice a day), then it will cost about $200 a month. He is worth it, it's just a shame it has to cost so much. I am sure it doesn't cost that much to make canine insulin and lower prices would make treating diabetes a more available option for pet owners. I can't imagine how many pets are rehomed, abandoned or put down due to unnecessary high costs of pet medication (I realize some meds are expensive, and they need to charge more, but at the same time, I am sure there are a lot of companies that charge a lot for the drugs just because they can).