When you receive the MO go to a Post Office (have ID with you) and get it cashed.

Bump, for money orders with an amount of less than $20 payable, ID is no longer required, as I discovered when I took one valued at $5.70 to the PO only last week.

And before you ask "who would be stupid enough to spend $8 plus postage to send me a money order worth just $5.70?", it was a postage refund from Australia Post themselves. 🙂