The last English king who stayed in the Tower was Henry VIII for the coronation of his wife Ane Boleyn. The Tower of London does not belong to the state it belongs to the British crown. It has been a World Heritage Site since 1988.
Tickets for Adults cost 27,50 pounds. Children pay 13,10 pounds and tickets for seniors and students cost 21,50 pounds. Tickets for the family ( 2 adults + 3 children or 1 adult + 4 children) cost round about 80 euros.
Here you can find out more informations about the tower or buy tickets:
https://www.hrp.org.uk/tower-of-london/#gs.bhwpvb