Flake foods sold for aquarium fish are VERY expensive! The so-called large economy size can easily be $36 a pound! What you’re really getting the most of is AIR and PACKAGING!
For many years I’ve been feeding my fish canned cat food — mostly 9 Lives and Friskies. You want to get the regular chopped (pate) without gravy. For most tropical fish, just place a small chunk or two in the tank. For very small fish, use a plastic knife to crush a little piece into small particles.
One downside when giving canned cat food to cichlids is that the big guys “chew” their dinner. This spreads a cloud of food bits into the water. If there’s a number of guppies in the tank, they will clean this up.