Hi and welcome to FDMB!
Read over this list of questions and pick some that matter most to you, especially where costs are concerned:
http://gorbzilla.com/questions_for_your_vet_.htm
The biggest initial costs are
The cost of the initial diagnosis.
The cost of insulin.
The cost of future vet visits.
What are not necessary to spend your money on:
Curves at the vet on a periodic basis.
Any prescription diet.
A "pet" blood glucose meter and test strips.
You can get a human glucometer very inexpensively, some companies even give them away.
The biggest cost associated with home-testing is the cost of the test strips. A meter such as the Relion meters sold at walmart will allow you to test multiple times a day for less than a dollar a day. Strips for specialty "pet meters" like the Alpha Track can cost $1 per strip!
Food - commercial grocery store or pet store foods, as long as they are canned and low-carb are fine for a diabetic cat. Fancy Feast, Friskees, Special Kitty, there are lots of them. Dry food is a no-no. "Prescription" foods like Hills, which many vets advise, are NOT good for a diabetic cat, even though they are marketed that way. And they cost an arm and a leg.
BG curves, which many vets insist are needed on an every week or two basis are NOT needed if you are testing your cat at home. Those also cost a lot of money.
Insulin - There are 3 types that we suggest using. Lantus, Levemir, and Prozinc. They aren't cheap. Prozinc can cost $100 a vial. The "L" insulin can cost twice that. But, they also last for a long time (months), so on a "per-day" basis, it really isn't a big cost. It just seems that way because you have to spend the money up front.
Hopefully that will get you prepped for your consultation. If you have questions after that visit, post them here and we'll help with that!
Carl