Just looking at what Chris Powell did with Charlton in 2011/12, by the end of August that season he'd shifted 12 out & brought no less than 17 players in!
Of those going out, they'd have picked up decent amounts for Carl Jenkinson & Rob Elliott (to Arsenal & Newcastle, repectively; both undisclosed fees). They weren't buying top level players - plenty of free transfers. Three disclosed fees, totalling about a million, & quite a few undisclosed (maybe Hamer from Reading, & Morrison from the pigs being notable, but not amounting to more than about 3 or 4 hundred thou between them, I'd have thought). Given that Jenkinson was rumoured to have cost more than £2m (I think?), the whole thing transfer-fee wise was probably self-funding.
But the point is that Charlton didn't spend any more than £2m by the looks of things on transfer fees (probably considerably less).
Of this fabled "£8 million" season's investment, assuming it continues apace next season, a quarter or less of it would need to be spent to match what Charlton shelled out to make themselves champions back in 2011/12. Is it too much to ask that that sum be committed by the owners/board to fund transfers in, & that they commit to not selling Adams/Sharp/Brayford (even of one or other of them indicates they might want to go)?
https://en.wikipedia.org/wiki/2011–12_Charlton_Athletic_F.C._season