No advice or knowledge about this topic, but I think you really should tell your parents! If they are contagious at all, then some of the 'small, filthy children' may have them as well. There may be ways to figure it out with the help of your parents without needing to spend tons and tons of money. If you were my child, I'd really want to know.
Good luck! And here is a link to one of my favorite health-focused resources: The Pinworm Thread May be some useful info there.