How to Use DontDestroyOnLoad on my C# Script?

Hey uhm, i do really need your help guys, I'm creating a shop script where the player can purchase a Power-Up( a coin-magnet to be specific), the situation is, the gameObjects are already placed on the terrain but they're not active. However, i have a shop scene and game scene. When the player purchase the power-up, then the gameObjects should become active and visible.

here is my code on the shop:

using UnityEngine; using System.Collections;

public class ConfirmScript : MonoBehaviour {

 public bool isMagnetBought = false;

 public void EnableMagnet(bool dec) {
     if(dec == true){
         isMagnetBought = true;
         DontDestroyOnLoad(this);
         Application.LoadLevel(6);
     }
 }

}

while this is the code in-game:

using UnityEngine; using System.Collections;

public class EnableMagnet : MonoBehaviour {

 public ConfirmScript cs;
 public GameObject magnet;

 void Start() {
     if(cs.isMagnetBought == true){ 
     magnet.SetActive(true);
     }
 }

}

and i received this error:

NullReferenceException: Object reference not set to an instance of an object EnableMagnet.Start () (at Assets/Scripts/EnableMagnet.cs:10)

which means i have an error on this line:

if(cs.isMagnetBought == true)

what could be the problem? I appreciate any help you can give. Thanks!!!