With so few birds and just that making you worry about the cost of feed and them not even full grown and laying yet, you might not be prepared yet for raising chickens. You go getting skimpy on feed and it'll show - they won't weigh well when it comes time for butchering (whether you're raising them for that or not) and the eggs will be fewer and smaller in size. If you need to try and supplement what amount of feed they get, kitchen and table scraps. If they're hungry, they'll eat most anything and they know what they can and can't eat far better than any human.