They are going to have to spend at least a billion to get near the top 4, unless they copy PSG and the free transfers high wages model. They will be under extra scrutiny, there's no way they can spend that over 3/4 years and still stay sweet with all the FFP regulations.. Newcastle are going to be looking at least 50/60m+ demands for every player they look for off other PL clubs, especially those from 5th to 10th - even if they go for the likes of Sarr, JWP, Raphina, Toney etc. they are going to end up spending big money on players that aren't of sufficient quality to get them into the Champions League to attract better players.
If they go down the PSG route and sign guys on free with big wages and signing on fees to sweeten the deal. There's a whole glut of players they can start to look at signing for free in January, Dybla, Kessie, Insigne, Sule, Christiansen, Zakaria, Cantwell, Boga, Isco, Sergi Roberto, Brozovic.