If his sugar is not under control, he needs another vet visit. He may need a different insulin. Getting his blood sugar under control is a must and is something you will need to work with your vet to accomplish.
As for diet...
I know the important thing is that the food needs to be low carb. Because of this, a canned-based diet is often preferred over a dry food diet. It's also important to put kitty on timed meals as this allows the medication to work best.
The cheapest option for canned food is Fancy Feast Classics (or the pate options.) You can certainly opt to chose a high quality of food if your budget permits.
As for diet...
I know the important thing is that the food needs to be low carb. Because of this, a canned-based diet is often preferred over a dry food diet. It's also important to put kitty on timed meals as this allows the medication to work best.
The cheapest option for canned food is Fancy Feast Classics (or the pate options.) You can certainly opt to chose a high quality of food if your budget permits.