I think CB isn't in that bad shape. If we re-sign Alcaraz for a season and bring in Browning for the first team, then we don't need to spend money on it.
We definitely need to have 3/4 adjustments though at least:
1. Robles being our #1 keeper
2. Konoplyanka. He looks really good, and is available for free this summer from memory. He'd be another addition of true quality and even in the worst case we'd easily sell him for 8-10m+ at least.
3. A real creative midfielder to play behind Lukaku. Barkley, with all the potential he has, doesn't yet create enough chances. This is a tough one as creative players aren't guaranteed to settle well so I'm not sure who'd we go for.
4. A striker to take the pressure off Lukaku. Whether it's McAleny or Long (personally think Long has got a much better chance), we need another striker and Kone is admittedly half useful so him, Lukaku + 1 should be enough.
#1 and #2 should take no more than £5m max of the budget with Kono's signing on fee.
#3 you could say up to £20m
#4 along with new contracts for a couple of players should take up the remaining 5m