Once you purchase the equipment and supplies needed to brew your own beer then it does become cheaper to brew your own beer at home.
Buying beer is more expensive than buying the ingredients and brewing your own homemade beer.
If you learn to brew the beer correctly then most times the beer you brew at home will be much better tasting than store bought beer.
I buy some beer but I also brew most of my beer and it tastes much better.
Although I'm not legally allowed to sell my homemade brewed beer without licenses I do sell some homemade beer I make at home to my friends because they get it cheaper and they love the fresher beer as well.
If you want to open a commercial beer company and brew and sell beer then you need a license and quite a bit of money.
But brewing beer at home is pretty cheap to get into and you'll enjoy cheaper and better tasting beer.