what brand cat food do you feed your cats? is the high cost really better. my cats are now eating purina kit n kaboodle. i was wondering if the high cost cat food is really better and would fill them up better so it would last longer. the science diet is $25 a 18 pound bag. i spend about $10 for the brand i use and buy a big bag about every 2 weeks. i would like to switch but can't really afford it unless it might last longer.