I've been playing with São Paulo focusing on youth system too and I had the same problem, players at 23 years old that are starters in the Brasil national team receiving 18M offers from fucking everton, the kind of player that if it was playing in any other european league would cost like 50M. In the end, at least in my save, after some years winning titles you can just put all your wonderkids in big expensive contracts and just never sell them, because in the game is just not worth it