This isn't an argument though, you'd have to try to claim that a new scheme with a president (or whatever idiotic scheme the ruling class tries to foist on people) would cost less.

Stripping most of that funding from the useless crown representative and entourage would be a great idea. Could be done tomorrow with acts of parliament and executive with no fanfare and no need for constitutional grandstanding. The fact they don't gives the imagination a good starting point for how much it would cost to be a republic.