How much do english mastiffs eat a month?

would you say like one or two normal sized bags a month and maybe..... like... can't they eat raw chicken a few times a month? i'm very interested in these dogs because my older siblings are moving out and i'm gonna be SUPER bored because i do everything with them. also i think my bro is taking his GSD with him and i love that dog so much! Also i will be an only child and I don't ask for much so all the food we buy them and clothes, and extras, they won't have to spend all that money and yeah... i have wanted a english mastiff for two year and there is a VERY famous mastiff breeder in my town. they bred one of America's most famous dogs.