Napoli didn't need cash to burn to win this Scudetto and neither did Milan spend a lot to win in 21-22.
I think we will mainly need a Skriniar replacement, a Dumfries replacement, a Gagliardini cm backup replacement, a Gosens replacement if he is sold and a Correa replacement.
Guerrero or Bensabini for lwb (both free agents), recall Agoume or the Reggina dude Fabian as backup cm, Thuram (free agent), rwb with Dumfries sale money, so really just spend for a CB and Marotta may even find someone cheap or free. We don't need a 100mill mercato to improve this squad.
Just remember that a flop like Gabigol cost Inter more than JZ+Maicon+Cambiasso+Julio Cesar+Lucio combined, so with smart spending you can build well. Biggest example is the joke Chelsea are now, it's not just about burning cash.
Milan had a net spend of around 80-90 million according to transfermarkt.
Napoli was basically at break even with their transfers. That's with selling Koulibaly and Fabian Ruiz for a combined 60 million while buying Kim and Kvaradona for 30.
I doubt it's very simple to replicate Napoli's success in the transfer market. If it was everyone would do it. On top of that we reportedly have to profit 30 million in the transfer market and we have Skriniar leaving on a free transfer.
No one is claiming that it's impossible to improve the squad and have a successful season in 23/24. Miracles do happen. But it's delusional to deny that the odds are stacked against us with the current financial situation.
Going out there and bringing in the next "JZ+Maicon+Cambiasso+Julio Cesar+Lucio" for peanuts is easier said than done.
Edit: I also think that your estimates regarding transfers are a bit conservative.
De Vrij's contract is expiring I believe. So I assume that he's a goner unless he accepts a pay cut. And we're already short stacked in defense even with Skriniar and De Vrij in the squad.
Same with Dzeko, not sure if he's got another season at the highest level in him.
Lukaku is also not a certainty next season, if he doesn't vastly improve during the last few months of this season Inter shouldn't even pursue extending the loan IMHO.