It's always nice to hear of new ways to save on postage costs but I think sending strikes using Media Mail will not work. The Post Office has a strict policy on what can be sent using Media Mail.
Here's what the USPS recommends sending using Media Mail;

Media Mail
Generally used for books (at least eight pages), film, printed music, printed test materials, sound recordings, play scripts, printed educational charts, loose-leaf pages and binders consisting of medical information, and computer-readable media. Advertising restrictions apply. There are presorted rates available for bulk quantities of Media Mail (minimum quantity is 300 pieces). There is also a barcoded discount available for Media Mail.