There are free flat-rate boxes and envelopes at the Post Office, and they can be ordered free from the postal service. UPS and FEDEX also offer free supplies to users with a free account.
Don't spend on new materials every time you ship. Reuse bubble wrap or packing peanuts -- you can even cut up a pool noodle to use and this can save you money!
Research Greyhound Package Express -- they have lots of deals to help you save including getting half off if you have six items or more. Plus college students get 15 percent off, and active military members and veterans can score 25 percent off.