Their wedding was similar in price to Kate and Willuams.The Royal Family needs security because they can be targeted for kidnapping, and because the family has needed protection from murderers throughout their existence.
"There were seven men in total who tried to stop Ian Ball, an unemployed labourer from north London, from kidnapping Princess Anne, Queen Elizabeth’s only daughter. A tabloid journalist, a former boxer, two chauffeurs and three policemen all faced off against Ball, but it was the princess herself, a force to be reckoned with in her own right, who kept Ball distracted from his goal,"
The Bloody Attempt to Kidnap a British Princess | History | Smithsonian Magazine
Harry's money comes from his father (£2.4 million annual allowance), his mother (£10 million inheritance) and his maternal great-grandmother (£5 million jewels inheritance). The bulk of Harry's money comes from his father. Over a period of 12 years, his allowance exceeds his inheritance.
Over-spending by Harry and Markle on wedding, clothing and house far exceeds all inheritance and annual allowance.
A little more on security and inflation.
I looked into the soveriegn fund and Frogmore was already in the master schedule to be restored as it was derelict. They spent money on top of that repair to actually remodel. Buckingham Palace is in the same cycle of restoration -and that project is for 370 million pounds.