I was reading through the forums on several shop sites, I sell on. A person was asking for help finding appropiate boxes to ship in for less money. I shared my tip with her and now for you.
1) Reuse old cereal boxes, cracker boxes, pasta and or microwave popcorn boxes. Be sure that all food particles and plastic bags have been removed before using the box. They are the perfect weight and size for first class shipping if you product is light weight. I usually recover mine with wrapping paper or copier papier if the box is small enough. Be sure to use a permant marker to stratch out the old bar code.
2) Call Wal-mart for when stocking is occuring. Most wal-marts will let you take their old boxes from stocking for moving.
3) Ship flat rate through the USPS. Its a little more expensive but they give you boxes upfront or will deliver them to your house. No joke.
4)Craig's list- a lot of people will advertise free boxes on there.