They were able to bring in several young players at prices that were not that expensive but within few years these young players could have extraordinary playing skills, this is why Serie A has team that has been able to win important competitions such as the UCL several times.
Look at how Juventus, Inter Milan, AC Milan always show their mainstay players, in the past, these three teams were the best at developing players and making the players become list of great European players.
I agree with you. In fact, I have never heard of a Serie A team that has a lot of money to buy star players. Many player transfer records are often broken by La Liga and English League teams. But they are still able to produce great players and become one of the best European leagues. Next season Italy has 5 clubs that will play in the Champions League. They are in second place for coefficients. This proves that Serie A clubs are great even though they do not have rich financial backing.
Strong finances and buying star players is not a guarantee for building a team and indeed we can see that the Serie A teams build a fairly even squad like what is happening now and also in the last few seasons we can also see that there is progress This is a significant thing that happened to the Serie A teams, several teams seem to have recovered better and because of this, it is also likely that Serie A will be more competitive in the next season.