The fine has to be more than the amount injected into the club - otherwise it's not a punishment or deterrent.They should be demoted back to Div 2 at the very least.
And have a 1bn fine.
It needs to be both a punishment and a deterrent to others.
They've spent around £1.5B on players since taking over, so I don't think it's excessive to assume they've injected somewhere around £2-3B. The fine would have to be more than that.