Hi there! I am pretty new to this myself but would advise you to take a look at
Dr. Lisa's food chart on
catinfo.org. That's the list most of us here use; we try to stay under 5% carbs ideally and definitely no more than 10%. Dry food is discouraged because even though a few varieties may be low carb, it is still moisture depleted and cats, especially diabetic ones, need more water than they're likely to drink from the water bowl. You say Toby is eating the wet food well, which is great! A lot of cats are hardcore kibble addicts and that makes things more difficult. The switch to a low carb, high protein all-canned diet can reduce the blood sugar by more than 100 points. When my Henry was diagnosed, he was at 465, and after a week on a diet of only Fancy Feast Classics he was down to 350--with no insulin (some people even see this kind of drop overnight). A lot of us feed Fancy Feast Classic pates, Friskies pates, or 9-Lives pates--they're all on the food chart I mentioned. So, as you can tell, you don't have to spend a fortune on food!

That said, I have recently started feeding some Weruva flavors to my diabetic boy in addition to his Fancy Feast, and it's a big hit with both him and my non-diabetic cat. Weruva and Hounds&Gatos are both listed on the chart, so just check the flavors to make sure you're feeding the best ones for Toby.
Has Toby started insulin yet? If not, now is a good time to go ahead and try the diet change, and then you and your vet can determine the appropriate starting dose based on his numbers on the new diet. If he has already started insulin, the process is a little different. If you could provide a little more info, like how much Toby weighs, what his blood sugar was at diagnosis, and what insulin he has been prescribed, that will help the experts here (which I am not!) advise you better on how much to feed, what would be a good starting dose, etc.
Finally, home testing is vitally important, so you'll see that mentioned here a lot. Most people use a human glucometer, such as the ReliOn from Walmart, since the test strips are much cheaper than those for the pet-specific meter (which I use...between that and the Weruva I will probably go bankrupt

). For example, if Toby has started insulin and you switch him to the wet food diet and his blood sugar drops 100 points because of the new food, you'll want to know that so you can make sure he doesn't drop *too* low (hypoglycemia, or "hypo"), which can be very dangerous. Did your vet mention home testing at all?
I'll stop there because I know there's a lot to process right now. But you're in great, capable hands here! Henry is already on his way to remission after less than a month on insulin thanks in large part to this community.