Thinking about opening a pay lake but have questions...?

I am thinking about puting in a paylake about an acer and a half, there are no others in this area that big.... But I have one important queastion. Where does your profit come from? I know you can make a profit because there are sevrel smaller ones here and there, But you have to pay for the fish (how much i dont know) then folks come by and catch them out..lol where is the profit comming from??? any one know? thanks