I agree that things don't look like they will be easy even for Allegri. Because we know that AC Milan will not spend large amounts of money to transfer players like the big teams from Laliga and the Premier League. However, we know that teams from Serie A are teams that are always able to bring in players who are not that expensive but of high quality, and sometimes they can increase the transfer value of players who are originally cheap to very high. So I hope Allegri is lucky with AC Milan next season. And yes, he has to think hard to find players who fit his criteria to revive AC Milan.
By the way Inter milan has lost in the UCL Final with a big score of 5-0. With this, none of the Italian teams managed to get a trophy from European competition this season.
With limited funds, promoting some young players to join the main squad is an option. As long as the player is able to provide strength for Milan. Buying young players who are not too expensive, could be an option too. I still remember De Ketelaere, he was young and good, but has been sold few seasons ago, Pioli did not give the right position for CDK, but was given the freedom according to his position by Atalanta. He also managed to grow under the right coach. if Allegri can do the same for young players, Milan should be able to makes young players growing with the team. Hopefully, Allegri is able to rebuild AC Milan, 2011 champions with an old squad, no one expected, but it happened. I don't expect too much next season, because i think, the important thing is Milan made a process of building a solid team for this season, maybe another next season Allegri has started to find the rhythm for Milan.