Do NOT use a regular letter envelope to ship your bracelets. The machines those envelopes go through are made for completely flat items, not bumpy bracelets. The bracelet may be damaged, or the envelope can rip open and the bracelet lost. Instead, use a bubble mailer (000 work well for me) and ship USPS first class. If you use paypal shipping, it will cost less than $2, including delivery confirmation.
I also put my bracelets in cellophane bags inside the bubble mailer for extra protection.