You can feed dry food, if that's going to be more cost effective with the food, but what you save on the food will be wasted plus even more money because you will likely need to give your diabetic more insulin.
You will also take a chance of your other cats becoming diabetic, and your cost for insulin will double.
If you look at the most recent food list compiled by Dr. Lisa Pierson, on catinfo.org, you can look through the list for foods under 10%, make a list of some or print out the list, then head to the store to see which is the cheapest wet food under 10% carb.
You may think the dry food is cheaper, but then you have to factor in the damage done to the cats' bodies and especially their teeth, the wet food is a pretty good deal.