caninsulin is much cheaper than lantus, but for cats the Lantus is much better. My understanding (and i can't say i know a lot about caninsulin) is that it was developed for dogs (hence the "canine" in the name). Diabetic dogs are incredibly different from cats. I know 3 people who have/had diabetic dogs. The vet figures out what the dose is and then they keep the same dose for the next 6-12 months before doing another curve. Most people don't even home test because dogs just don't vary as much. They don't metabolize insulin in the same way that cats do. Cats have very fast metabolisms, which is why the Lantus/Lev are one shot/24 hrs in people, but one shot/12 hrs in cats. Caninsulin doesn't last as long in cats as it does in dogs.
One thing we know about cats is they do best when their blood sugar is tightly controlled, especially if they are kept in normal non-diabetic numbers. The longer-lasting insulins, Lantus and Levemir, are especially good in that respect.
If you're looking for a slightly cheaper option, Levemir costs a little bit less than Lantus and the dose is typically a little lower. I didn't open Whitey's ss to look, but if you were giving (just for an example) 3u Lantus to whitey, we'd suggest you start at 70% of that, or 2.0u. Cobb went from 31uLantus to 22uLantus and had roughly equivalent blood sugar control. Might be an option for you.
Another option is to look on Craigslist. You've gotta be careful and check out the story of why the insulin is for sale, and also check the expiration date & ask if it was kept refrigerated, but i bought 4 boxes of Lantus pens for about $250 a couple of years ago. I was buying from a woman whose diabetic dad had passed away. The insulin was totally fine. Others have had success with that, but you do need to ask questions and be confident about what you're buying.
There are also some pharmacies that will sell one pen at a time - especially if that pharmacy serves hospitals and nursing homes. You just have to call around and ask - there's no rhyme or reason. Some individually owned, some corporate pharmacies will break the boxes up. some won't.
I'd definitely stick with Lantus or Lev though, for Whitey's sake. They're simply better for cats. Prozinc is another good option.