VBA: Auto-fill cells based on user defined values and quantity

Try:

Private Sub Submit_Click()
    Application.ScreenUpdating = False
    Dim LastRow As Long
    LastRow = Cells.Find("*", SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row
    Dim x As Long
    For x = 2 To LastRow
        Cells(x, 1).Resize(, 2).Copy Sheets("Output").Cells(Sheets("Output").Rows.Count, "C").End(xlUp).Offset(1, 0).Resize(Cells(x, 3))
    Next x
    Application.ScreenUpdating = True
End Sub

See next code

Option Explicit
Private Sub Submit_Click()
Dim WsIn As Worksheet
Dim Wsout As Worksheet
Dim LR  As Integer, I  As Integer
Const FR  As Integer = 2
Dim Rg  As Range
    Set WsIn = Sheets("Input")
    Set Wsout = Sheets("Output")
    With WsIn
        LR = .Cells(Rows.Count, "C").End(3).Row
        For Each Rg In Range(.Cells(FR, "C"), .Cells(LR, "C"))
            Rg(1, -1).Resize(1, 2).Copy
               Wsout.Cells(Rows.Count, "C").End(3)(2, 1).Resize(Rg, 1) _
                   .PasteSpecial Paste:=xlPasteValues
        Next Rg
    End With
    MsgBox (" Job Done")
End Sub

Mumps1
That's awesome! Thank you.

I'm impressed with how few lines of code it ended up being.

How hard would it be to have it only paste as values and not carry over the formatting?

Try:

Private Sub Submit_Click()
    Application.ScreenUpdating = False
    Dim LastRow As Long
    LastRow = Cells.Find("*", SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row
    Dim x As Long
    For x = 2 To LastRow
        Cells(x, 1).Resize(, 2).Copy
        Sheets("Output").Cells(Sheets("Output").Rows.Count, "C").End(xlUp).Offset(1, 0).Resize(Cells(x, 3)).PasteSpecial xlPasteValues
    Next x
    Application.CutCopyMode = False
    Application.ScreenUpdating = True
End Sub

"only paste as values and not carry over the formatting?"
The code sent, only copies values ...just try it !

Glad to help.

Just for reference was also cross-posted here