I have been a couple of swaps, and I have gotten different prices on mailing the same package at different post offices. The different prices had to do with the thickness of the envelope. I had ordered the flat rate tyevek envelopes from the post office website, and stuffed it full of 2.5" squares and it cost $6.00 to go from NY to Tx... I'm talking about the envelope looked like it was going to explode. The clerk taped it.. I also pack my swaps in a ziplock bag, and put my address on it. If the bag eplodes, or gets ripped apart, the chances are that it will get back to me.. the thought of spending time on making the project, and it getting lost will upset me big time..