We could use Portugal experience. They invested 650 mio.Eur into 7 new stadiums and reconstruction of 3 big ones (Dragao, Da Luz and Alvalade) and about 150 mio Eur went into infrastructure. It´s 800 mio Eur of investment which brought jobs for 4000 people, about 500 thousand visitors spent a lot of money for accomodation, food, beverages and tickets.
Bottom line: gayinings were about 800 mio.Eur. Quite a balance in comparison with expenses.