How do I ask parents for loan?

I'm 13. I earned (over the summer) $150 from mowing lawns/washing cars around the neighborhood. I want an mp3 player that is around $170 (SanDisk Sansa e260) How do i go about asking for the money? I'm definitely not part of a rich family, more middle-class. Or should I wait until Christmas? I am fairly shy, you could say. Thanks in advance!