Turns out the fine appears to only be $300. That could easily be taken care of without actually having to pay using proper procedure.
Payment of Postage
Recipients should not submit any mail without postage to a mailbox, according to the USPS Recipient Services (3.1 Use for Mail). This includes items the sender places inside the mailbox, attaches to the mailbox or hangs outside the mailbox. If a letter carrier finds materials in a mailbox without postage, he can charge the recipient for it.
Distributing flyers or other forms of mail in mailboxes is against the law. In Chapter 83 of "Crimes and Criminal Procedures" on the Justia U.S. Laws website (Title 18, Section 1725), it states that a person who distributes flyers in mailboxes must pay a fine. This law gives the U.S. Postal Service ownership of mailboxes. As of 1994, the cost of the fine was $300. This law includes the illegal distribution of bills, accounts, money, circulars and any other mail.
Removal of Flyers
If a person puts flyers in mailboxes, residents may remove them, since they might consider them "junk mail." The recipient of the flyers can also take legal action against the sender.http://www.ehow.com/list_7216408_conseq ... ilbox.html