The cost of shipping in a priority mail package weighing 1 pound* is about $3.61 each way, so a total around $7.50. If you do priority mail, it's double that. The envelope is free, however. If someone wanted to use 1st class and buy their own envelopes, they could save by doing that. They could do that, couldn't they, if they provided a stamped, self addressed envelope with their charms? I believe the shipping time is the same.
That would pay for 2 more 1/2 yards of fabric (I shop the sales).
bkay
* a priority mail package with 140 5" charms (including all the baggies) and a return envelope weighs 15.4 oz.