Scrolling Inventory - Instantiate Buttons Too Slow [UI 4.6]

Hi there,

//==== What I'm Looking For ====//

I'm trying to make a popup scrolling inventory like this:

[ElderScrolls Online Inventory]

http://cdn.tentonhammer.com/sites/default/files/styles/large/public/257080.jpg?itok=qRxbwZAb

//==== What the Problem Is ====//

The problem is that when I instantiate the buttons, the frame rate drops and it takes longer to load, the more items it has to load into the scene for the inventory. This is already a problem at 10 items, nevermind 50. How can I make a scrollable inventory that can be sorted/categorised without this problem?

//==== What I Have ====//

At the moment I have 3 item category options which are individual lists:

 var itemCategory1            : List.<Item> = new List.<Item>();
 var itemCategory2            : List.<Item> = new List.<Item>();
 var itemCategory3            : List.<Item> = new List.<Item>();
 
 var itemCategorySelected    : List.<Item> = new List.<Item>();

when I click on a button it will set the selected category to match the item category.

 function ButtonSelectCategory1 ()            
 {
     itemCategorySelected = itemCategory1;
     LoadInvBoxs();
 }

This is the function I use to instantiate the boxes. I've striped out setting values etc for offset to make it easier to read. The inventory Button prefab has a script attached that has an item variable that gets filled in depending on the item it's creating. So that when I click the button it can identify what item it represents.

 function LoadInvBoxs()
 {
     itemCount = itemCategorySelected.Count;                    // sets the amount of items to match the number of items in the selected category.
     
     itemPrefab = Resources.Load("UI/InvBox", GameObject);    // sets the prefab to instantiate to the inventory Box Prefab.
     
     // Sets variables for width, height, ratio, row count etc added in here.
 
     var j : int = 0;     
     for (var i = 0; i < itemCount; i++)
     {
         if (i % columnCount == 0)
         {  
             j++;
         }
             
         //create a new item, name it, and set the parent                
         var newItem = Instantiate(itemPrefab);
         newItem.name = scrollableArea.gameObject.name + " item at (" + i + "," + j + ")";                            // sets new objects gameobject name.
         newItem.GetComponent(ItemInventoryData).item = itemCategorySelected[i];                                        // fills in the variables on the button to match itemCategorySelected.
         newItem.transform.GetChild(0).GetComponent(Text).text = newItem.GetComponent(ItemInventoryData).item.name;     // sets new buttons text to match name of the item it represents.
         newItem.transform.parent = scrollableArea.gameObject.transform;                                                // sets the parent.
         newItem.GetComponent(UI.Button).onClick.AddListener(newItem.GetComponent(ItemInventoryData).ClickItem);        // adds the function that the button should use when clicked.
 
         // sets transform of the object and it's offset added in here.
 
     }
 }