5600X is just too expensive at the moment, still selling in massive numbers...... maybe when Alder Lake launches.
5600G, yeah maybe close enough if you're careful with the board, if you find something like this in stock somewhere.
I have seen some 5600G on a large site i cannot mention here that are somewhat cheaper than the 5600X, comes to £310 5600G + that Asus board. His original option was £280.
I would still go for the 10400F TBH.
It’s just about doable. TBH I’d go with AM4.