Convertir numero en dinero, get money c#

Elementos que vamos a necesitar;

Código del programa;

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace WindowsFormsApplication1

{

    public partial class Form1 : Form

    {

        string Reverse(string str)

        {

            string res = "";

            for (int i = str.Length - 1; i >= 0; i--)

            {

                res += str[i].ToString();

            }

            return res;

        }

        //================================================

        string Money_Text(string str)

        {

            string rev = Reverse(str);

            string res = "";

            int f = 0;

            for (int i = 0; i < rev.Length; i++)

            {

                f++;

                res += rev[i].ToString();

                if (f == 3)

                {

                    res += ",";

                    f = 0;

                }

            }

            return Reverse(res);

        }

        public Form1()

        {

            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)

        {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)

        {

          

        }

        private void button1_Click(object sender, EventArgs e)

        {

            textBox2.Text = Money_Text(textBox1.Text);

        }

    }

}