for an idea like this, the cereal wouldn't be your money maker - just your draw and appeal. You'd only be making $1-2 profit per BOX of cereal at MOST, but you could charge $2.99 for milk, coffee, redbulls or orange juice ($0.50 a
refill if staying to eat) and thats where most of your revenue / profit would come from. Your overhead could be small because you'd only be open from 5 or 6 am to 10 am every day. Have other sides of hashbrowns, bananas, donuts etc - breakfast food (no pancakes or waffles otherwise you'd just be a bootleg denny's and lose your identity and appeal/uniqueness)
send out flyers to schools + organizations in schools "$1 breakfast on way to class! Stop by
@Taadow cereal shop" and then tax them mafukkas on everything else

wouldn't even mention any other thing on the marketing aspect, just hit people with it when they arrive