Sorting repeater value by dropdownlist

Question

here is my problem, I have repeater control which shows products and prices and also have dropdownlist with value low to high,high to low. i want to sort repeater value by price low to high and high to low from selected value in dropdownlist .

     <asp:Repeater ID="rpt3"  runat="server">
         <ItemTemplate>


         <div class="col-lg-3 col-md-6 mb-4">
            <div class="card h-60">

               <asp:Image ID="Image1" class="card-img-top"   ImageUrl='<%#Eval("pic1", "pics/{0}") %>' Height="160px"   runat="server" />

        <div class="cardnew" >
              <p class="name cap"   style=" font-size: 12px;margin-top:0px"> <%#Eval("name") %></p>
               <p class="card-title name cap" style="color: #000000; font-size: 15px;width:auto;margin-bottom:2px;margin-top:5px"><%#Eval("adtitle") %></p>
                 <asp:Image ID="Image2" CssClass="imgn"  ImageUrl="~/images/Star_Gold-512.png" Height="20" Width="15" runat="server" />
        </div>

      <div class="card-footer" style="text-align:center">
              <p>Starting From : <%#Eval("rate") %> </p>
      </div>
    </div>
  </div>

       </ItemTemplate>
         </asp:Repeater>

Code Behind

     SqlConnection myconn;
    SqlCommand mycomm;
    myconn = new     SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
    string q = ("SELECT postad.adid, postad.adtitle, postad.rate,postad.name, postad.date, postad.pic1, addstate.statename, addcity.cityname, addsubcat.scatname, addcat.catname FROM addcity INNER JOIN addstate INNER JOIN addsubcat INNER JOIN postad INNER JOIN addcat ON postad.cat = addcat.catid ON addsubcat.subcatid = postad.scat ON addstate.stateid = postad.state ON addcity.cityid = postad.city WHERE (postad.scat = @scat) and (postad.expiry >= Getdate()) and postad.status='Approved'");
    mycomm = new SqlCommand(q, myconn);
    mycomm.Parameters.AddWithValue("@scat", Request.QueryString["scid"]);

    DataTable dt = new DataTable();
    SqlDataAdapter da = new SqlDataAdapter(mycomm);
    myconn.Open();
    da.Fill(dt);
    if (dt.Rows.Count > 0 && dt.Rows[0][0] != string.Empty)
    {
        rpt3.DataSource = dt;
        rpt3.DataBind();
    }
    else
    {
        rpt3.DataSource = null;
        rpt3.DataBind();
    }
    myconn.Close();