Usando il seguente codice.
<?php
$prezzo=499.00;
?>
<form>
<select name="qt" size="1" onchange="document.getElementById('prezzo').innerH TML = <?php echo"$prezzo*10"; ?>">
<?php
$sql_reg = mysql_query("SELECT DISTINCT Nome FROM zone ORDER BY Nome");
while ($data = mysql_fetch_object($sql_reg))
{
echo "<option value=$data->Nome>$data->Nome</option>";
}
?>
</select>
</form>
Costo totale: <span id="prezzo">0</span></p>