The box is free. You get it at the post office. Fill the box then either buy the postage online and print and paste it or go to the post office and pay and send it. You can schedule a pickup or hand it to your mail carrier if they are in a truck but I prefer to take mine in. I just sent one out today- medium size- filled it to the brim and it was $10.xx to send. I will be shipping it back later (I sent it ahead to an exhibition) and while I was at the post office I pre-purchased the postage sticker to send it back and got an extra label and filled it out. This way I will be able to refill, seal, put on label and postage and send out. Easy! I did have to resist the temptation of putting rocks in it just because it said not weight limit. In the end I thought that preserving the poor carrier was more important than my sense of humor.