They cost a lot more than £100 million. I think the Queen gets a Sovereign Grant of around 86 million per year and she pays people like Edward (£400k per year) out of that, staff costs and maintenance of buildings.George Osborne also gave the Queen the rights to the seabeds 12 miles off the coast, so the Queen has been quids in raking in royalties and fees from off shore wind turbine companies. Organising the Sovereign Grant rather than paying the Royals through the Civil List netted them a big increase.
That figure doesn't include all the monies that Charles is gifted each year by having the Duchies of Cornwall and Lancaster as his source of income from the "nation" - that totals around £40 million per year - he gives William about 3-4 million from that , William also has all his costs for appearances/events/staff etc paid for out of the SG. Charles gives Harry money out of the Duchy income.
The security costs for the RF are insane - 24/7 groups of protection officers for close family and officers when minor royals attend events, estimated costs at up to 100 million per year but the police won't reveal an actual figure (it was stated that when Beatrice and Eugenie's 24/7 security ended back in 2011 it was costing 500k a year) Andrew was extremely annoyed that he had to fork out for it going forward privately with money from the Queen.
They also get grants from the Government to help with refurbs etc. and pay "peppercorn rents" on "grace and favour" properties. For example, Andrew was able get a 75 year lease on 30 room Windsor Lodge (valued at £30 million) for £1 million. Despite "Edo" being a "property developer and interior designer" he and B seem pretty happy availing themselves of cheap digs in Kensington Palace.
Local councils ( and therefore us peasants)also have to pick up the tab when they visit anywhere.
They are parasites. It's the 21st century we should no longer be doffing the cap or rewarding people just because they had the great good fortune to be born into extraordinary wealth and privilege. The Queen certainly doesn't have to spend days on a trolley in an A&E corridor or wait for many hours lying cold and in pain for an ambulance to arrive like many of our elderly population. A "skeleton"(volunteer) staff of 22 was needed to look after her during lockdown.No wonder she looks good at 96!
Tourists will come to the UK whether we have a RF or not. We could open up more of the Palaces if they weren't around (Like France).
www.instituteforgovernment.org.uk/explainers/royal-finances