barri the postage will all depend on how you pack the envelopes, the thinner the cheaper on postage. they have to fit through the first class letter slot for the lower fees or the envelope gets classified as a package and the postage costs more.
someone mailed me ps squares in one of the card sized envelopes (i.e. birthday card) instead of a legal sized one so she was able to spread them all out for the lower postage. i never thought to use the card sized envelopes as they are taller and have more room to spread the squares out.
with practice you will learn to package the envelopes thinner for the lower postage.
