For Datagrid the event is 'ItemDataBound' and for Gridview the event is 'RowDataBound'.
sample:
protected void DataGrid_ItemDataBound(object sender, DataGridItemEventArgs e)
{
Textbox tbx1 = (TextBox)e.Row.FindControl("ActualCostTextbox");
Textbox tbx2 = (TextBox)e.Row.FindControl("EstimatedCostTextbox");
if (tbx1 != null & tbx2 != null)
{
}
}