In my job as an online retailer/wholesaler, I ship a variety of merchandise to both domestic and international locations. To minimize the cost of my shipping materials, I have always relied on Hefty's Air Kraft economy bubble mailers. They are available in a range of sizes, from 000, which at 4" x 8" is the ideal size for a small item like jewelry, to #7, which is 14 1/4" x 20". The latter is the size we use to ship several t-shirts or an adult size Halloween costume to our retail customers.
The mailers have a convenient self-seal, which means I don't have to mess with tape guns to close the packages when they are ready to leave our warehouse. And the bubble lining in each puncture-resistant mailer does double duty: it helps to seal the contents against moisture as it cushions and protects them during processing and shipping.
A case of the smallest mailers contains 250 mailers and costs $30. A case of #7 mailers (the largest size) contains 50 mailers, and costs $40. For a truly economical solution to your shipping needs, these mailers are the way to go!