Ok cool, as I said i'm not an expert on USPS.

If stamps aren't suitable, what about sending well concealed cash instead?

Any piece of mail that is over 13 ounces (which the magazines i plan on mailing are) is enelgible for first class mail. The stamps that one would normally purchase at a United States post office can only be used for first class mail. Once an item goes over 13 ounces it becomes priority mail (which normal stamps dont cover).

I'm in the UK so not an expert on usps. But I don't understand why you say stamps are out of the question? If it's due to the value involved then a quick look on the website shows they sell stamps worth $1, &2,$5 and $10.

Mailing from the United States and the return would be from there as well.

It would help to know which country you are in and which country your sase is coming back from.

Does anyone have experience with purchasing online postage for their Self addressed stamped envelopes. The reason i ask is because when purchasing postage online you have enter the mailing date, which is kind of hard to determine (as some signers take a few days to a few months). I plan on mailing a few different magazines which are over 13 ounces so stamps are out of the question. Thank you in advance!