Not thinking of a very ambitious market. Here's what we can do.
GK - no change, maybe a new backup keeper
Spend - 0
Defence - no big changes, a new backup defender, maybe Vanheusden
Spend - <10m
Wingbacks - release Young, get Dimarco, keep Perisic.
Spend - <10m
Midfield - sell Gagliardini, Vecino, Vidal+Nainggolan (release). Sign a starting quality MF (de Paul/Locatelli), and a backup midfielder.
Spend - <25m (Gags + Vecino should fetch about 20m, and the mentioned MFs can be got for <40m)
Forwards - get Dzeko, sell Pinamonti
Spend - 0
Without Vidal, Nainggolan, and Kolarov, we free up good wages that can go for Dzeko and others. Overall, this provides more competition for starting spots, and good backups for all positions. This can be done with a spend of ~25mn based on how we deal.