admission: the amount of money that you pay to go into a building or to an event
admission charges/prices But if admission = the amount of money, why would you need the word "charges" or "prices", which also refer to the amount of money? I think admission simply means entry into a building (in your context), and charges/prices/fees are the money that is charged for that entry.
£5 admission On a sign in the ticket window, it is clear that £5 is the cost of admission.
What's the admission? Here, too, if you were standing at the ticket window and asked "What's the admission?" it would be very clear that you were asking about the price of admission. But if you said to someone in the street, "I love the Louvre" and they responded "What's the admission?", that would be a strange conversation...