$string = '1 990';
$number = str_replace(' ', '', $string);
echo $number; // 1990
$string = '<span class="price-value">1 990</span>';
$substring = preg_replace('#<span[^>]*?>(.*?)<\/span>#si', '$1', $string);
$number = str_replace(' ', '', $substring);
echo $number; // 1990