The Royal Family carried out around 3000 engagements last year. These included community visits, meeting visiting heads of state, investitures, garden parties etc. It doesn't include the weekly meetings with the PM, approving legislation or other constitutional duties. You may think these unnecessary or pointless pageantry, but successive governments have agreed that these are appropriate activities for the head of state. They are not of a nature which directly generates income for the country, but indirectly they contribute to international relations, and community visits and garden parties help to boost morale within the UK.

If you don't like that, campaign for change to elect a government which will get rid of it, as may happen soon in Australia. However I think you'll find that an elected president has a very similar workload. Take a look at the Irish president's engagements for example and you'll see they are of a very similar nature.

Steve is concerned that the money "doesn't rightfully belong to him", but it goes to him only in the same way as a government department's budget goes to the Secretary of State. The money is to cover the costs of the king's official duties. It doesn't go to the king personally. As far as I am aware he isn't paid a salary for performing these official duties, and his personal expenditure comes out of his private income.

You seem to have an inflated idea of his personal wealth. The Sunday Times Rich List estimates his personal wealth at £600m. That's a very tidy sum, but it's capital, not income. He could not "well afford" to pay £125m a year. Do the sums.

To repeat, these are the facts:

The Crown Estate belongs to the state, it is not the personal property of the monarch. 100% of its profits go to the Treasury, and its board is answerable to parliament. For those calling for it to be nationalised, that has effectively been the position since the eighteenth century.

The Sovereign Grant does not come out of general taxation but from the profits of the Crown Estate.

The Sovereign Grant is to cover the costs of the official duties of the monarch. It does not go to the king personally. It is overseen by trustees who are also answerable to parliament. Any surplus does not go into the king's pocket but to a reserve fund.

The Sovereign Grant amounts to around 0.01% of all public expenditure. Any changes to it either way don't materially affect the public finances. There are many respectable arguments for getting rid of the monarchy, but the cost savings to the public purse would not be noticeable.