The amount of feed that they consume as young - adult age depends on a lot of things. Depending on their breed / size, how much they get to free range for other food, what else you are feeding besides pellets (table / garden scraps), living conditions (hot / cold) will all determine their food requirements.
I have 6 Rhode Island reds that have pellets available all the time, get a handful of greens each day, and can free range almost every day for a few hours to all day (depends on our schedule as we do not let them free range without supervision...hawks, coyotes, skunks, ...) I also give them an occasional bowl of table leftovers, yogurt, fish, ...whatever is soon to go bad from the fridge.
My birds will go through a 50# bag of layer pellets in 4 weeks during the coldest part of the winter or when they are molting. Otherwise the 50# bag seems to last about 6-7 weeks. I've also discovered (I am fairly new to this myself) that raising the feeder reduces waste. And keeping rodents, dogs, cats, etc out of the food makes it last lots longer.
There is also a wide variety of price for layer pellets depending on where you live and the choices / brands available. We basically have two brands so they are competitively priced to be within a few $$ of each other, both running around $12-14 for 50#. But I've also heard that the West Coast charges a bit more than other parts of the country, so yours may be cheaper.
