How to get value from database and + with value in textbox?

 <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" SelectCommand="SELECT * FROM [delikatesse]"></asp:SqlDataSource>
            
            
           <div id="ekstra_vare">
                <asp:DataList ID="VisDeli" runat="server" RepeatLayout="Table"
RepeatColumns="4" DataSourceID="SqlDataSource1" OnItemDataBound="VisDeli_ItemDataBound" CellSpacing="5" CssClass="tabel1" >
                    
                    <HeaderTemplate>
                        <p class="overskrift_bestil">Vælg tilbehør</p>
                    </HeaderTemplate>
                    
                    <ItemTemplate>
                 
                          <td><asp:TextBox ID="TextBox_deli" runat="server" Width="15" Height="15"></asp:TextBox></td>
                          <td><p><%#Eval("deli_navn") %></p>
                              <td><p><a class="email" href="#emailpopup?deli_id=">info</a></p></td>

                
                             
            </div>
                               
             

                          </td>
                    
                       
                    </ItemTemplate>
                </asp:DataList>

</div>
            <asp:SqlDataSource ID="SqlDataSource3" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" SelectCommand="SELECT * FROM [kurve] WHERE kurve_id = 1"></asp:SqlDataSource>
       
            <div id="ekstra_pris">
                <asp:Repeater ID="Repeater2" runat="server" DataSourceID="SqlDataSource3">
                    <ItemTemplate>
                        <%#Eval("pris") %> kr.
                    </ItemTemplate>
                </asp:Repeater>
                <asp:Label ID="Label_Vispris" runat="server" Text=""></asp:Label>
                <asp:Button ID="Button1" runat="server" Text="Opdater" OnClick="Button1_Click" />
                 </div>      

protected void Button1_Click(object sender, EventArgs e)
   {
       int totalvaerdi = 0;

       List<ValgtDeli> valgteDeli = new List<ValgtDeli>(); //Her laver jeg en liste over valgte frugter. Det er et nyt objekt, som kan indeholde påde ID, Navn, Antal og Værdi



       foreach (DataListItem item in VisDeli.Items)
       {
           if (item.ItemType == ListItemType.Item || item.ItemType == ListItemType.AlternatingItem)
           {
               TextBox Textbox_antal = item.FindControl("TextBox_deli") as TextBox;


               int pris = 149;

               int prisVare = ;

               int enkeltFrugtAntal = int.Parse(Textbox_antal.Text);


               totalvaerdi = pris + enkeltFrugtAntal;


           }

       }
       if (totalvaerdi > 0)
       {

           Label_Vispris.Text = Convert.ToString(totalvaerdi);
       }



   }