It is true that fish don't eat everyday in the wild. But you have to relize that your fish are not in the wild. They are exposed to a completly diffrent eviroment. No matter how hard you try to replicate thier natrual habitat you won't get it completly correct. Now I'm not bashing anyone's feeding habits. I just don't think comparing aquarium fish to wild fish is appropriate. They are in two completly diffrent places, with completly diffrent aspects affecting the fish. Feeding is a strange creature, in that everyone has a diffrent experience on it. Sometimes it works to feed only every so often, somtimes more regular feedings work. As long as your fish are getting fed, I think that is the main point.
And really, fish food isn't that expensive. Flake and freeze dried can be bought and extreamly cheap prices. It is almost a steal, so price shouldn't be a concern. And, you fish should only be fed enough that they can clean up. The best way to figure this out is to use a styrofoam cup. Cut it in half and put it in the water. Put the food in the water and see how long it takes them to eat it all. You should really work on not overfeeding your fish. How often you feed them doesn't affect your water quality, it is how much left over food settles to the bottom. And if you mix the right fish together there shouldn't be any food debris left over.