<form id="form1" runat="server">
 <asp:GridView ID="GridView1" AutoGenerateColumns="False" ShowHeader="True" runat="server" OnRowDataBound="GridView1_RowDataBound">
  <Columns>
   <asp:BoundField HeaderText="Name" DataField="Name" ReadOnly="true" />
   <asp:BoundField HeaderText="Amount" DataField="Amount" ReadOnly="true" />
   <asp:TemplateField HeaderText="CheckBox">
    <ItemTemplate>
     <asp:CheckBox ID="gridCheckBox" runat="server" />
    </ItemTemplate>
   </asp:TemplateField>
   <asp:TemplateField HeaderText="TextBox">
    <ItemTemplate>
     <asp:TextBox ID="gridTextBox" runat="server"></asp:TextBox>
    </ItemTemplate>
   </asp:TemplateField>
  </Columns>
 </asp:GridView>
</form>

<script type="text/javascript">
<!--
function gridCheckBoxOnClick(elementRef, textBoxId, amountValue)
{
 document.getElementById(textBoxId).value = (elementRef.checked) ? amountValue : '';
}
// -->
</script>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
 if ( e.Row.RowType == DataControlRowType.DataRow )
 {
  // The Name is in bound column #0
  //string nameValue = e.Row.Cells[0].Text;

  // The Amount is in bound column #1
  string amountValue = e.Row.Cells[1].Text;

  // CheckBox with an ID of "gridCheckBox" is in column #2 of the Grid
  CheckBox gridCheckBox = (CheckBox)e.Row.Cells[2].FindControl("gridCheckBox");

  // TextBox with an ID of "gridTextBox" is in column #3 of the Grid
  TextBox gridTextBox = (TextBox)e.Row.Cells[3].FindControl("gridTextBox");

  if ( (gridCheckBox != null) && (gridTextBox != null) )
  {
   gridCheckBox.Attributes.Add("onclick", string.Format("gridCheckBoxOnClick(this, '{0}', '{1}');", gridTextBox.ClientID, amountValue));
  }
 }
}