My response to that would be if we line-up right now in formation, RB and LB are the position MOST clearly where we are lacking quality.
Midfield needs depth and probably a top level midfielder, yes. But even with a midfield of Pogba/Locatelli/Zakaria or Pogba/Locatelli/McKennie or Pogba/Locatelli/Rabiot is better than whomever lines up at LB/RB. Those two spots we have nothing. We have provincial level players playing there. And in a 4-3-3 formation (im assuming) where the fullbacks can provide so much threat both in attack and support in defense, I think having BOTH sides be glaring drops in quality compared to the rest of the squad makes both the clear places where improvement in mandatory and firstmost.
In my mind I say Sandro replacement isn't a priority right now BECAUSE he is unsellable and gonna be on last year of his contract so unless we pay him to leave we'll have to do with having him.
So again in my foolishness I'd keep funds for midfield and winger and start with Danilo as LB and Cuadrado as RB. Sandro/Pellegrini and De Sciglio as back ups.
I know it's not optimal but at least Danilo/Cuadrado aren't crappy duo.
Next year with Sandro and Cuadrado gone we can rebuild and invest money on those positions.
Right now I'd focus on midfield and a winger.
Namely : Pogba ,Milinkovic and Fratessi in trade off Rabiot,McKennie and Arthur (I don't consider Ramsey as a player)
For winger position the best shot avaible would be Osmane Dembelè if he doesn't sign for PSG. Then there are options like Manè,Gnabry and so on
And we'd need a Vlahovic reserve like Arnautovic. Aka a experienced but cheap option to leave on the bench + Di Maria