How many pages are there in Princess Diaries 4.5?

There is no "Princess Diaries 4.5". The series consists of four books:

1. The Princess Diaries

2. The Princess Diaries 2: Royal Wedding

3. The Princess Diaries 3: Princess in Training

4. The Princess Diaries 4: Royal Wedding

There are also two companion books:

1. The Princess Diaries: The Royal Wedding Album

2. The Princess Diaries: Royal Wedding Planner

If you're referring to something else, please provide more context.