Cron job running out of memory very fast

Cron job running out of memory very fast

I am hosted on godaddy shared hosting. My database has over 500 entries,
but I expect it to be much higher as time go on. Maybe in the thousands. I
have this running as a cron job, but it runs out of memory (64 megs) after
only 33 records. I can not change the max memory since I am on shared
hosting. Is there anything I can do to reduce the memory usage? Perhaps
any way to clear the memory each time it loops?
include('simple_html_dom.php');
$html = new simple_html_dom();
$price_query = mysql_query("SELECT * FROM prices");
while ($price_rows = mysql_fetch_assoc($price_query))
{
$vendor_id = $price_rows['vendor_id'];
$product_id = $price_rows['product_id'];
$product_page = $price_rows['product_page'];
$product_string = $price_rows['product_string'];
$product_array = $price_rows['product_array'];
if (urlOK($product_page))
{
$html = file_get_html($product_page);
$new_price = $html->find($product_string);
$new_price = preg_replace('/[\$,]/', '', $new_price);
$product_price = $new_price[$product_array];
$product_price = strip_tags($product_price);
$qry="UPDATE prices SET product_price='$product_price' WHERE
product_id = '$product_id' AND vendor_id = '$vendor_id'";
mysql_query($qry);
}
else
{
$qry="UPDATE prices SET product_price='0.00' WHERE product_id =
'$product_id' AND vendor_id = '$vendor_id'";
mysql_query($qry);
}
$vendor_id = null;
$product_id = null;
$product_page = null;
$product_string = null;
$product_array = null;
$qry = null;
$html = null;
}
This is the 1 function im calling:
function urlOk($url)
{
$headers = @get_headers($url);
if($headers[0] == 'HTTP/1.1 200 OK') return true;
else return false;
}