Guest room price query

As a University College (a registered Charity) our students are allowed to rent a guest room for their personal guest (up to 3 nights). They do so by filling out the guest room book, which at the front has a list of prices for the rooms. Also the students have handbooks which are changed each year to make up to date (this information is also available on the College intranet). Unfortunatley the price for guest room in the handbook was not updated last year and is incorrect. A student is now quoting contract law and saying that we must charge the lower incorrect price as that is one of the advertised prices. Is this correct or as the price given in the guest room book is the correct one?