From an ask reddit thread:
I send all my mail for free. The trick is to switch where you write your address with with where your sending the mail to, and vice verca. Then you "forget" to put a stamp on it, and drop it into a usps mailbox. (One of the blue ones, not your home mailbox) Make sure you send it about 10-14 days before you want it to arrive. When the mailperson picks up your letter, he/she will notice there is no stamp and return it to the "sender". It works EVERY time. I haven't bought stamps in over 4 years. I actually stumbled across this on accident when sending my Grandma a birthday card while being a half-retarded adult who doesn't understand how to live on my own.
Do with it what you will...
you could also just pay the $0.49, seeing as they are actually providing you a service