High quality foods without fillers and byproducts will give your dog more energy and overall better health. Regardless of what brand of food you feed, portion control is what will keep your dog slim. The feeding guidelines on the back of the bag are almost always excessive.
What are you currently feeding? Some affordable high quality foods are Diamond Naturals, Kirkland (this is Costco's store brand), and Merrick's Whole Earth Farms line.
Some good foods on the lower end of the price scale are Canidae and Taste of the Wild. Both are pretty easy to find and quality foods, in my opinion. Portion control, as mentioned above is how to get your dog to lose weight.
There are lots of ways to slim down a chubby dog! first find a low carb, high protein food, second daily exercise, 3rd portion control. you may want to ask your vet what they recommend.... you don't want your pup to be hungry all the time but most people feed their dogs more than they really need.