Show only Message from ApplicationException
static void getBookInfo(Book book)
{
    bool isNumeric;
    float number;
    string numberInput;

    Console.Write("Enter Book Title: ");
    book.Title = Console.ReadLine();
    Console.Write("Enter Author's First Name: ");
    book.AuthorFirstName = Console.ReadLine();
    Console.Write("Enter Author's Last Name: ");
    book.AuthorLastName = Console.ReadLine();
    Console.Write("Enter Book Price: $");
    numberInput = Console.ReadLine();

    isNumeric = float.TryParse(numberInput, out number);

    if (isNumeric)
        book.Price = number;
    else
    {
        throw new ApplicationException
        (
            "This is not a number!n" +
            "Please try again."
        );
    }
}

using System;

namespace Lab_6
{
    class Program
    {
        static void Main(string[] args)
        {
            Address address = new Address();
            address.StreetNumber = "800";
            address.StreetName = "East 96th Street";
            address.City = "Indianapolis";
            address.State = "IN";
            address.ZipCode = "46240";

            Book book = new Book();

            try
            {
                getBookInfo(book);
                book.PublisherAddress = address;
                book.PublisherName = "Sams Publishing";

                Console.WriteLine("----Book----");
                book.display();
            }
            catch (NegativeInputException ex)
            {
                Console.WriteLine(ex.Message);
                return;
            }
            catch (ApplicationException ex)
            {
                Console.WriteLine(ex.Message);  // I had to change so I have only this,
                                                // instead of whole printout.
                return;
            }
        }

        static void getBookInfo(Book book)
        {
            bool isNumeric;
            float number;
            string numberInput;

            Console.Write("Enter Book Title: ");
            book.Title = Console.ReadLine();
            Console.Write("Enter Author's First Name: ")
            book.AuthorFirstName = Console.ReadLine();
            Console.Write("Enter Author's Last Name: ");
            book.AuthorLastName = Console.ReadLine();
            Console.Write("Enter Book Price: $");
            numberInput = Console.ReadLine();

            isNumeric = float.TryParse(numberInput, out number);

            if (isNumeric)
                book.Price = number;
            else
            {
                throw new ApplicationException
                (
                    "This is not a number!n" +
                    "Please try again."
                )
            }
        }
    }
}

if (isNumeric)
{
    book.Price = number;
}
else
{
    MessageBox.Show("This is not a number!n" + "Please try again.");
}

try
{
    getBookInfo(...)
}
catch (ApplicationException exception)
{
    MessageBox.Show(exception.Message);
}

try
{
     Book myBookParameter = .....;
     getBookInfo(myBookParameter);
}
catch(ApplicationException x)
{
     MessageBox.Show(x.Message);
}