Welcome! My cat Willie was diagnosed on December 7th, and I remember how completely overwhelmed I felt. We found our way to here, and the folks here have been absolute angels to us, and in that short 3 months, I've seen my Willie's health make a dramatic improvement. It's also amazing how what seemed so scary... ear pokes and insulin shots... has just become part of our normal everyday routine.
I would echo what others have said... the three keys to start really are: 1) a diabetes-friendly diet (wet food that is low in carbohydrates); 2) hometesting to ensure your cat's safety and understand how the insulin is working in their system; and 3) a long-acting insulin with a proven track record in treating feline diabetes. Others are right... if your vet should prescribe Lantus or Levemir, the pens are a much more economical option... just be sure to make it clear to the pharmacist that you do NOT need the pen needles that humans use, but rather you need some U-100 3/10cc insulin syringes, preferably with half-unit markings on them. The pens come in a 5 pack that usually sells for $175-250 in the US, depending on the area. Many here order from canadian pharmacies at a much lower cost. Also, if you have a Costco nearby, many of their pharmacies will sell the pens individually. While it doesn't really "save" you money, it does help to stretch out the payments for supplies. You don't have to have a Costco membership to use their pharmacies... it's the law. If you don't have a Costco, many hospital outpatient pharmacies will sell you individual pens as well, so it is to your advantage to call around. Be sure to take advantage of any prescription discount options you might have... for example, AAA offers discounts at many pharmacies.
If money is tight, there are definitely ways to keep costs under control. If you look in the Calculating Carb % sticky, there is a link to Janet & Binky's food charts, which will help you to pick out foods that are low in carbohydrates. We generally recommend a carb % of no higher than 10%, but many of us stick to under 5% as a general rule. There are TONS of economical options on the list, including Sophisticat (petsmart), special kitty (walmart) or friskies/9 lives.
If you have access to a Walmart, the relion syringes work quite well and are very affordable. Many of us here use their Relion home testing meter ($9) which has very affordable test strips ($20 for 50 or $12 for 20), but other stores also have economical options. Many of us get strips online for similar or cheaper prices as well. The last thing you'll want to pick up is some ketone strips. It is important to test your cat's urine for ketones regularly when first getting started. Ketones in the system can lead to Diabetic Ketoacidosis (DKA), a very dangerous and often fatal condition for diabetic cats. Regular ketone testing will help you detect ketones right away and treat them before they turn into something serious.
Websites such as Hocks.com or americandiabeteswholesale.com are excellent sources for supplies, as is ebay.
While this new chapter in your life may seem like a scary one, you're in the right place. With the resources here, you can walk into your vet appointment well educated about how to best help Hunter achieve better health. You're on that path now, and Hunter is very lucky to have a human that is so committed to his care that she is scouring the internet looking for information about his condition.
Please feel free to ask lots of questions... we're happy to help!