My 5 year old male cat, Blackie has been diagnosed with diabetes. I am feedind him Dm wet food 2xs a day with his insulin injections of 4. I have the dry DM food out all the time since i have 5 other cats. Is there a better dry food? Is there a less expensive wet food? I also read that i could purchase insulin from WalMart. What do you think? Any suggestions and advise is appreciated.