UI elements not accessible due to protection level

I've been struggling with this error for a few days now and can't find a way out ... I've searched on the forum and found that this error should be caused by the property being private but in my case i switched everything to public and still no good. I've tried inserting constructors and whatnot , now I need your help please.

Btw it's a clicker project I started to learn how to use Unity

Main File-----------------------------------------------------------------------------------------------------------

 using UnityEngine;
 using System.Collections;
 
 public class InitScript : MonoBehaviour {    
 
     public UnityEngine.UI.Text goldText, BonusInfoText, GPSText;
     public float gold = 0, GPC = 0, GPS = 0;
     public GPCUpgrade pioche = new GPCUpgrade(){name="Pioche",baseCost=100,cost=100,bonusPower=1, level=0};
     public GPCUpgrade chariot = new GPCUpgrade(){name="Chariot",baseCost=100,cost=100,bonusPower=1, level=0};
     public GPCUpgrade dynamite = new GPCUpgrade(){name="Dynamite",baseCost=100,cost=100,bonusPower=1, level=0};
     //public GPSUpgrade mineurs = new GPSUpgrade("Mineur",15,15,0.1f,0);
     //public GPSUpgrade mineurs = new GPSUpgrade(){name="Mineur",baseCost=15,cost=15,bonusPower=0.1f, level=0};
 
     void Start () {        
         InvokeRepeating ("Tick", 1.0f, 1.0f);    
     }
 
     void Update () {
         pioche.bonusPower = 0;
         goldText.text = "Gold\n" + Mathf.Floor(gold);
         BonusInfoText.text = "Gold par click : " + GPC+ "\nGold par seconde : " + GPS;
 
     }
 
     private void Tick(){
         GPS = (Mathf.Round (GPS*10))/10;
         gold += GPS;
     }
 
     private void GoldClick(float gold, float GPC){
         gold+= GPC;
     }
 
     private void GPCClick(float gold, float GPC){
         
     }
 
     private void GPSClick(float gold, float GPS){
 
     }
 
 }
 

Class File ------------------------------------------------------------------------------------------------------

 using UnityEngine;
 using System.Collections;
 
 public class GPSUpgrade : MonoBehaviour {
 
     public string nom = "";
     public int baseCost = 0;
     public int cost = 0;
     public float bonusPower = 0;
     public int level = 0;
     public UnityEngine.UI.Button btn = new UnityEngine.UI.Button ();
     public UnityEngine.UI.Text GPSText=new UnityEngine.UI.Text(){text=nom + "\t\t\t LVL " + level + "\nCost : " 
                                                             + cost+ "gold \nGain ; "+ bonusPower + "GPS"};
     
     /*public GPSUpgrade(){
 
     string nom = "";
     int baseCost = 0;
     int cost = 0;
     float bonusPower = 0;
     int level = 0;
     UnityEngine.UI.Button btn = new UnityEngine.UI.Button ();
     UnityEngine.UI.Text GPSText=new UnityEngine.UI.Text(){text=nom + "\t\t\t LVL " + level + "\nCost : " 
                                                             + cost+ "gold \nGain ; "+ bonusPower + "GPS"};
     }
 
     public GPSUpgrade(string vnom,int vbaseCost, int vcost, float vbonusPower, int vlevel){
         string nom = vnom;
         int baseCost = vbaseCost;
         int cost = vcost;
         float bonusPower = vbonusPower;
         int level = vlevel;
         UnityEngine.UI.Button btn = new UnityEngine.UI.Button ();
         UnityEngine.UI.Text GPSText=new UnityEngine.UI.Text(){text=nom + "\t\t\t LVL " + level + "\nCost : " 
                                                                 + cost+ "gold \nGain ; "+ bonusPower + "GPS"};
     }
     */    
     public void Clicked(float gold, float GPS){
 
         if (gold >= cost) {
             gold -= cost;
             GPS += bonusPower;
             level++;
             cost = Mathf.FloorToInt(baseCost * Mathf.Pow(1.15f,level));
         }
     }
 }