Welcome to the family!
I, personally have a household of 13 cats...yes you read that right...13... :lol: As well as a 95lb dog, and I'm a stay at home wife, fur-mom, and full time college student as well as a mother and grandmother. So I understand budget concerns, some of the best tips I can give you to keep everyone fed, and still keep the budget under control as well as providing the best possible care for your extra sweet Louie would be:
1) Learn to test at home, not only does this make sure that Louie is getting the right amount of insulin it also keeps dollars in your wallet since you won't have to drag him into the vet all the time to have curves done. Plus curves at the vet's are pretty much useless since stress raises BGs and all cats are under some kind of stress in going to the vets. Just think how much you hate going to the doctor, regardless of how nice your doctor is, kind of the same thing for out kitties.
2) Don't get the prescription cat food, there is plenty out there with the same or better ingredients on the commercial market, we feed all 13 of ours just plain old Friskies Pate style canned food.
3) request a nice long lasting gentle insulin, the 3 best are Lantus, Levermir, & PZI, and ask that your vet write the script for the solostar or flexpens. Now while the sticker shock is pretty steep upfront, you get 5 pens and that, if handled correctly will last you almost a year, and you should be able to use it to the very last drop.
Also you will want to start at a nice low safe dose...usually between .5u to 1u twice a day or b.i.d. It can always be raised if it isn't enough, but testing will tell you that.
4) Breathe...and ask a ton of questions...It will get easier I promise, in fact so easy that I adopted not 1 but 2 of my cats as diabetics from this very board.

Maxwell is already in remission and has been there a year as of this coming Nov. 1st, and his newly adopted sister Musette is trying her best to make it there as well. It is possible with a short course of insulin and a good low carb/high protein diet that Louie too will go off insulin, and even if he doesn't , testing and giving insulin will become as routine as brushing your teeth and brushing your teeth will probably take longer.
Mel, Maxwell, Musette & The Fur Gang