First, take a breath. Managing your cat's diabetes is incredibly overwhelming -- at least at the very beginning. I promise; it will become routine. Well, it will become routine in a couple of weeks. It takes a bit of perseverance. All of us have been in your shoes. I was a wreck when Gabby was diagnosed and I am very comfortable with medical information. It didn't help in the least. In fact, the vet apparently figured that I knew how to give an injection and never showed me what to do and I was so in shock I didn't ask. YouTube was a huge resource. We're here to help.
There is a website that can help you locate cat only vets/clinics. This is the link to the search for a
cat friendly practice (American Association of Feline Practitioners). While a new vet may want to re-run some labs, if Jayden's lab work is recent and was sent out to a commercial lab (e.g., Idexx), if you tell the vet that you are on a budget, they may be OK with using at least some of the existing labs. However, there's no way to know that. Like any medical professional, the vet doesn't want to do anything that could harm your cat since lab values can change, although given how recent the diagnosis was, it's not terribly likely that there will be a big change.
You have lots of options for what t feed Jayden. Most of the so-called prescription foods have nothing in them that is truly medically necessary for diabetes. In fact, the Royal Canin dry food is quite high in carbohydrates. Diabetics require a low carbohydrate diet. We consider low carb as under 10% although most of the members here feed their cats foods that are in the neighborhood of 5% carb. However, as Wendy noted, you really need to be home testing before you change Jayden's diet. This is a great website dealing with
feline nutrition. The website also has a
chart listing most of the canned food available in the US along with the carb counts for those foods. There's a lot to choose from. A good portion of the members here feed their cats either Fancy Feast of Friskies pate style food and it looks like you already decided that those are good options for Jayden. You can feed both of your cats the same food. It will make life much simpler if you do.
There is a weight-based formula for the initial dose of Lantus. The formula is: initial dose = 0.25 x ideal weight in kg. For Jayden, the maximum dose would be 2.0u. If tends to be easier on the caregiver's nerves if you start your cat out on a lower dose and work your way up based on what home testing tells you about how the insulin in working. If you want to do more reading, there are several sticky notes at the top of the
Lantus forum that describe how Lantus works, dosing methods, etc.
Please let us know how we can help make this easier.