I used to buy the Tetra Cichlid sticks that I feed in 3 pound boxes, but they are no longer available in bulk, I have to buy the large cans instead, which kind of sucks because it was cheaper to buy it in the 3 pound boxes by far.
however, my LFS during boxing week always has fish food 50% off all week.
so in the past I will buy 4 or 5 large cans of tetra colour bits, 2 cans of wardley shrimp pellets etc etc. all at once.
so I might spend $150 but I get $300 worth of food which pretty much lasts me the whole year. I will do the same this year.
as far as feeding goes, I only feed until they are visibly full. there should be a bulge in the belly.
you should be able to look at the fish and tell that it just ate. thats enough.
any more and you create more headaches with water quality issues and go through food quicker than you really need to.
hope this helps.