$new_string = str_replace($what_to_replace, $what_to_replace_it_with, $old_string);
EDIT: To replace data, you need preg_replace()
. In your case to remove "price_range" and all numbers and underscores directly after it, use this:
$new_string = preg_replace("/price_range[0-9_]+/", "", $old_string);