procedure Form1_OnShow (Sender: TObject; Action: string);
begin
  Form1.ComboBox1.TagString:='itemA';
  Form1.ComboBox2.TagString:='itemB';
end;

procedure Form1_ComboBox1_OnChange (Sender: TObject);
var
i,j:integer;
begin
  Form1.Edit1.Value:=0;
  for i:=0 to Form1.ComponentCount-1 do
      if (Form1.Components[i] is TdbComboBox) then
          for j:=0 to TdbComboBox(Form1.Components[i]).Items.Count-1 do
                if TdbComboBox(Form1.Components[i]).ItemsChecked[j]= True then
                  Form1.Edit1.Value:= Form1.Edit1.Value + SQLExecute('SELECT price FROM "'+ TdbComboBox(Form1.Components[i]).TagString +'" WHERE id='+IntToStr(TdbComboBox(Form1.Components[i]).dbIndexToID(j)));
end;

begin

end.