Put this note into the bubble mailer with the CDs. Do NOT seal the Bubble Mailer. Take a large Tyvek envelope and put an address label on it FROM you TO the trader. You can also write the information directly on the envelope, if you prefer. Take both of these envelopes to your local post office, or proceed as listed below if you already know postage rates.
Some people send their stuff from work, where they have a postal scale in shipping.
You can also take the materials to a local commercial shipping center, like Mailboxes Etc., but you'll need to actually watch them to ensure that they do everything correctly. Often, the person doing the work will not be the person you talk to. Ask if they can take care of it while you're there, or go elsewhere. If you find that your packages always cost the same to mail, just use stamps in that amount. Metered Postage BAD .