Give this a try. Next time, try formatting your code where it is easier to read, too.
<form action='processprices' method='post' name='FormName'>
<input type='submit' name='priceform' value='Update Prices'>
<?php
$result = mysql_query("SELECT productid, model, modelnumber, price, active
FROM products WHERE productcompany='$_POST[productcompany]' ORDER BY materialid, price desc");
// start a counter in order to number the input fields for each record
$i = 1;
while ($prices = mysql_fetch_array($result)) {
?>
<table border='1'>
<tr>
<td width='60'>
<?php echo $prices['modelnumber'] ?>
<input type='hidden'
name='<?php echo productid[$i] ?>'
value='<?php echo $prices['productid'] ?>' />
</td>
<td width='250'>
<?php echo $prices['model'] ?>
<input type='hidden'
name='<?php echo model[$i] ?>'
value='<?php echo $prices['model'] ?>' />
</td>
<td>
<input type='text'
size='15'
name='<?php echo price[$i] ?>'
value='<?php echo $prices['price'] ?>' />
</td>
<td>
<select name='<?php echo active[$i] ?>' size='1'>
<option value='1' <?php echo $prices['active']? 'selected' : '' ?>>Active</option>
<option value='0' <?php echo !$prices['active']? 'selected': '' ?>>Not Active</option>
</select>
</td>
<tr>
<?php
// add 1 to the count, close the loop, close the form, and the mysql connection
++$i;
} // while ($prices = mysql_fetch_array($result))
mysql_free_result($result);
?>
</table>
<input type='submit' name='priceform' value='Update Prices'>
</form>
BTW, take out one of the submit buttons, too.