We are about to hit a new wave of impoverishment which could make austerity so far seem like the warm up act.
We need the RF pruned right back, so direct line only (though waiting for retirement age for the Princess Royal and the Wessexes, rather than abrupt severance). This does of course mean there will be fewer Royal charitable patronages (which personally I think is a great shame, but I've seen so many posts here saying that would be unimportant that I'm going with that view in times when we are broke)
Revenues of the Duchies of Lancaster and Cornwall could be redeployed so the Sovereign Grant can be (voluntarily) lowered (for a specific time)
The difference in cost between household security for household largely based in UK and working here, and the actual international costs should be borne by the couple, not the Duchy nor the taxpayer.
We shall all be too broke, with too many areas of life to be mended, to want anything spent on this.