public partial class _Default : Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            grid.DataSource = GetProducts();
            grid.DataBind();
        }
    }

    IEnumerable<ProductModel> GetProducts()
    {
        var products = new [] { 
            new ProductModel{ Id = 1, ProductName = "Монитор", Price = 5000, Amount = 5 },
            new ProductModel{ Id = 2, ProductName = "Видеокарта", Price = 7000, Amount = 3 },
            new ProductModel{ Id = 3, ProductName = "ЖД", Price = 3000, Amount = 0 },
        };
        return products;
    }
}

public class ProductModel
{
    public int Id { get; set; }
    public string ProductName { get; set; }
    public decimal Price { get; set; }
    public int Amount { get; set; }
    public string AmountText 
    { 
        get
        {
            return Amount == 0 ? "Отсутствует" : null;
        } 
    }
}

public class ProductModel
{
	public int Id { get; set; }
    public string ProductName { get; set; }
    public decimal Price { get; set; }
    public int Amount { get; set; }

    public string AmountText 
    { 
        get
        {
            return AmountVisible ? "Отсутствует" : null;
        } 
    }

    public bool AmountVisible 
    { 
        get
        {
            return Amount == 0;
        } 
    }        
}

<table>
        <tr>
            <td>1</td>
            <td>Монитор</td>
            <td>5000</td>
            <td></td>
        </tr>
        <tr>
            <td>2</td>
            <td>Видеокарта</td>
            <td>7000</td>
            <td></td>
        </tr>
        <tr>
            <td>3</td>
            <td>ЖД</td>
            <td>3000</td>
            <td>
                <span style="color: Red;">Отсутствует</span>
            </td>
        </tr>
    </table>