The coronation is going to cost around £100 million

In the 18th century there were four coronations, three in the 19th century, and four in the 20th. It is likely that there will be no more than four this century. Taking the Irish model of electing a president for a seven year term, this gives 14 elections in 100 years.

The Electoral Commission gives the cost of the 2016 Brexit referendum as £129 million. The 2015 UK general election cost around £115 million. This should allow a reasonable estimate of the cost of a presidential election to be made. This is without the pomp and ceremony of inauguration.

Some of the presidents could be returned unopposed, which would reduce costs, but even a lavish coronation would seem to be value for money when it comes to choosing a head of state.

Every UK taxpayer pays £2.40 every year towards the upkeep of the royals

The office of President doesn't come without running costs. There will still be the need for security, posh limmos, state banquets, foreign trips to represent the country, pensions for life after leaving office, etc.

It would be interesting to know how many elected heads of state leave office poorer than when they went in.

DC