The cost of publishing a book in the UK can vary significantly depending on a number of factors, such as the type of book, the length of the book, the number of copies you plan to print, the format of the book (e.g. paperback, hardback, ebook, etc.), and whether you plan to self-publish or go through a traditional publishing house.
That said, there are some general ballpark figures you can keep in mind. For instance, if you self-publish a standard novel-length book (80,000 words) as a paperback, you can expect to spend around £2,500 on printing costs alone. If you go the traditional publishing route, you may not have to pay any upfront costs, but you will likely give up a larger percentage of royalties.