Why would security costs be an argument against the monarchy? Arguably we don’t spend enough money on protecting people in power - 2 MPs murdered since 2016. The senior working royals have protection because there are people who want to harm them. Anyone in a position of power becomes a target. France, US, etc all spend loads on protecting their leaders.
I’m not convinced by the whole money argument in general. Everything comes down to… why only the monarchy?
We spent money on the funeral and coronation: we also spent public money (including on security) on hosting the Olympics, the Euros, Eurovision, the rugby World Cup, the Ashes, the cricket world cup, there’s the annual New Years’ blow-out, we’ve spent public money celebrating Pride, carnival, Christmas, Diwali. The idea of spending money on things which are fun, celebrate our heritage, and boost our standing in the world is not crazy or unique to a monarchy. Inaugurations in G7 countries don’t come cheap.
We spend money on preserving historical palaces, yep. We also spend public money on preserving our national parks, national trust properties, historical waterways, even our ‘henges’ whatever they are. There are stately homes which are privately owned, as the palaces would be if we sold them, and their owners no longer have the kind of wealth required to maintain them and so they fall into disrepair.
I suppose it comes down to what kind of country we want to live in. We could live on the cheap - we could move our government from prime London properties onto a concrete industrial estate, we could spend no money on anything fun or just nice, we spend no money on protecting people when lives are at risk, we could withdraw from the world stage and become neutral on things like Ukraine and human rights abuses in the Middle East and China, which would really take the target off the backs of our leaders & mean we can have them for pennies. I just don’t want to live in a cheap country at the end of the day. We’re in one of the wealthiest nations on earth, we should use the voice we have on the world stage even if it means our leaders need us to protect them from harm, we should have big events like coronations or inaugurations that show us off and project our soft power, we should invest in the arts and heritage not go urrrghhhh the upkeep on these palaces is a lot, let’s convert them all into flags and flog them to some oligarchs…
I don’t really think that’s anything to do with having a monarchy or not though. We could in theory move the royal family onto a newbuild housing estate of affordable homes, but that wouldn’t make our country look great.