$d = new DOMDocument();
$d->loadXML($xml);
$x = new DOMXPath($d);
$result = $x->evaluate("//text()[contains(.,'617.99')]/ancestor::*/@id");
$unique = null;
for($i = $result->length -1;$i >= 0 && $item = $result->item($i);$i--){
    if($x->query("//*[@id='".addslashes($item->value)."']")->length == 1){
        echo 'Unique ID is '.$item->value."\n";
            $unique = $item->value;
        break;
    }
}
if(is_null($unique)) echo 'no unique ID found';