Trying To Get My BF To Eat Healthier

My boyfriend of four years suffers from Congestive Heart Failure, Lupus and Rheumatoid Arthritis. I've read studies that a healthy diet will help him greatly. I know he hears me, but I don't think he's listening.

I've tried making him healthy meals as often as I can, but we live off of food stamps, disability and what I make working as a cashier at Winn Dixie. Which isn't a lot in the long run.

We buy what's on sale, but it isn't always the healthiest of things. Does anyone know stores where I can buy healthy food for cheap prices or has really good sales?