Stamps.com Vs buying my own stamps

Hey guys.
Soon I intend on launching a marketing campaign, which consists of mailing manilla envelopes (9 by 12) with about 7 pieces of paper within.
My question to you: Do you think that stamps.com would be cheaper than buying my own stamps?
Do you have experience direct mailing? If so, how much do you think it would cost to mail a manilla envelope with 7 pieces of paper?
What would you do to get these out?
I appreciate your time guys.
PS: All mail is USA domestic

See original post by sarevok