Here's the link for the
Lantus Savings Card. When you complete it, note that your "child" is 18. I'm sure in people years s/he is!
Some pharmacies will sell just one pen out of a box. You have to call around - sometimes hospital pharmacies will, sometimes chains or locally owned - there is no rhyme or reason. Costco will in one city and not in another, but it's worth making the phone calls.
This link on
Lantus/Levemir, Info, Proper Handling & Storage specifically mentions Lantus being repackaged by vets as not being good. It doesn't address compounding, although I understood that Lantus is still under copyright for a little while longer (although I'm thinking this summer might be the expiration of that). Read through this page and watch the video on how to draw up your insulin to keep it from getting contaminated so it lasts as long as possible.
Cats that are newly diagnosed that get into Tight Regulation (having their blood sugar held between 50-120) as quickly as possible have the best possible chance of healing, going off of insulin and becoming diet controlled. Given that, I wouldn't even consider trying insulin that might not be as effective as just buying a pen or vial. There is a pdf about 5 paragraphs down from the top of the
Tight Regulation Protocol page that explains how this works. That's the protocol most people follow on this insulin support group, although there are a few that don't.
If your cat is diagnosed but not on insulin yet, you'll want to switch to low carb canned food asap, start hometesting and then start the insulin asap. It doesn't help them to sit in high numbers any longer than absolutely necessary.
We're glad to give you a hand - just ask your questions. There are no dumb ones - we've all been new and in your shoes as well.