cek pinjaman dan harga taksir

<!-- cut here -->
<form name="input_data" id="input_data" action="insertpinjaman.php" method="post">
<table border='0' border='#CC3366' cellpadding='3' cellspacing='0' style='border-collapse:collapse'>
  <tbody>
    <tr>
      <td>No.Pinjaman</td>
      <td><input type="text" name="id_pinjam" required value="<?php echo kdauto("pinjaman","P"); ?>" readonly /></td>
    </tr>
    <tr>
    <tr>
      <td>No.Nasabah</td>
      <td><select name="no_nasabah" required="required">
      <?php
      $no_nasabah= mysql_query("select no_nasabah from nasabah");
      while ($row = mysql_fetch_array($no_nasabah)){
        echo "<option value =$row[no_nasabah]>$row[no_nasabah]</option>";
      }
      ?>
      </select>
      </td>
    </tr>
    <tr>
       <td>Barang</td>
       <td>
         <select id="barang"  name="barang" required="required">
         <?php
          $tipe= mysql_query("select tipe,hargataksir from nilaitaksir");
                $hargataksir=array();
          while ($row = mysql_fetch_array($tipe)){
                    $hargataksir[]=array($row[tipe],$row[hargataksir]);
              echo "<option value='{$row[tipe]}'>{$row[tipe]}</option>\n";
          }
        ?>
        </select>
      </td>
    </tr>
    <tr>
      <td>Pinjaman</td>
      <td><input type="text" name="pinjaman" id="pinjaman" maxlength="100" required="required" /></td>
    </tr>
    <tr>
      <td>Tanggal</td>
      <td>
    <input type="date" name="tanggal" maxlength="100" required="required" value="<?php echo date('Y-m-d'); ?>" />
      </td>
    <tr>
    <td>Status</td>
      <td>
        <select name='status' required="required">
          <option value='Belum'>Belum</option>
      </select>
      </td>
    </tr>
    <tr>
      <td align="right">
        <input type="button" id="submit" name="submit" value="Simpan" onSubmit="javascript:cek_harga();"/>
      </td>
      <td>
        <input type="button" value="Batal" onClick="self.history.back()">
      </td>
    </tr>
  </tbody>
</table>
<script>
<?php
echo "var hargataksir=new Array();\n";
foreach($hargataksir AS $data)
{
  echo "hargataksir['".$data[0]."']=".str_replace('.','',$data[1]).";\n";
}
?>
  $(document).ready(function(){
    $('#submit').click(function(){
      if(parseFloat(hargataksir[$('#barang').val()])>=parseFloat($('#pinjaman').val()))
      {
        $('#input_data').submit();
      }
      else
      {
          alert('terlalu besar');
      }
    });
  });
</script>
<?php
//-- CATATAN
* form ditambah attribute 'id="input_data"'
* input type="submit" diganti input type="button" dan ditambah attribute 'id="submit"'
?>

//--untuk sisi server-nya bisa dibuat:
<?php
//panggil file config.php untuk menghubung ke server
include('conn-db.php');
//tangkap data dari form
$harga_taksir = $_POST['harga_taksir'];
$id_pinjam = $_POST['id_pinjam'];
$no_nasabah = $_POST['no_nasabah'];
$barang = $_POST['barang'];
$pinjaman = $_POST['pinjaman'];
$tanggal = $_POST['tanggal'];
$status = $_POST['status'];
$jatuh_tempo = date('Y-m-d',strtotime('+30 day',strtotime($tanggal)));
$sql="IF NOT EXIST(SELECT 1 FROM  nilaitaksir WHERE hargataksir<$pinjaman AND tipe='$barang')
      INSERT INTO pinjaman
      (id_pinjam, barang, no_nasabah, tanggal, tanggal_perpanjang, pinjaman, status, jatuh_tempo)
      VALUES
      ('$id_pinjam', '$barang', '$no_nasabah', '$tanggal', '$tanggal', '$pinjaman', '$status', '$jatuh_tempo')"
$query = mysql_query($sql) or die(mysql_error());