There are a number of rewards and benefits to keeping a backyard flock of chickens. They do provide you with wonderful, fresh eggs daily. They also give you plenty of fertilizer (manure) which is a rich source for your compost bins. Chickens will eat pests and pick emerging weeds from the lawn.
There are a few cons to owning a backyard flock, as well. First of all, if you plan to allow your chickens on the lawn just be apprised that they will strip all the greenery fairly quickly (unless allowed limited free-range time). Next, sanitation is important to the health and well-being of the flock. Chickens produce a lot of dust from feather preening and waste. It is a personal decision on how often to clean the coop and run area, but if you really want to keep it "pristine" it takes a good deal of time and effort. -requires daily scooping and regular cleaning. Finally, know your breeds and climate. Choose appropriately. Shade and fresh, cool water are crucial in hot climates. In very hot climates, it requires changing water frequently throughout the day to keep it cool (and keep the chickens from experiencing heat stroke).
The cost to raise a flock varies. Consider housing. It can be as elaborate or minimal as desired. Repurposed materials can be utilized at little to no cost for a good coop, or elaborate plans or shed kits can be purchased and customized which requires an investment. Feed is another consideration. The cost varies by the product choice - organic/non-GMO v. conventional. There is a large difference in the price of each.
Research and inform yourself before undertaking raising a backyard flock and make a sound, measured judgment on whether it is right for your climate, lifestyle, and budget.