Yes. Your price updates in real time as you build your book, so you'll always see your current total before checkout. How it changes depends on where you live:
In the United States: books are priced by page-count range, so your price only changes when your book moves into a different range. Adding or removing a few pages within the same range won't change it. Learn more in How is my Classic Book price determined? (United States)
Outside the United States: books are priced per page, so your price changes a little with every page you add or remove. Learn more in How are my Classic Book and Luxury Layflat book prices determined? (International)